I brought this up in another thread, but I think this issue could use its own.
I took over DMing Expeditions for my FLGS mid-February. Of the six sessions I've run, every single table has included new players. Many of them had never played an RPG in their lives, and for most of them, this weekly event is their only exposure to the game. I'm thrilled to introduce people to D&D, but I don't feel like Expeditions is the best venue to do it, especially since it is billed as "for advanced players."
The game store has us on a 3-hour time slot. I've requested another hour, but have yet to hear back from the owner. If granted, this will allieve some of the problems, but not all. The additional needs of new players makes completing an Expeditions module in one sitting especially difficult. I can pare down a module (as suggested in the other thread) in an attempt to get through it, but reviewing new characters, answering questions, explaining rules, checking their dice rolls, reminding them of simple table etiquette time and again, etc... Altogether, it eats up a lot of time. It's an exhausting process week after week, I'm at my wits end dealing with a few personalities, and four of the veteran players found other venues play at.
FWIW, one of the vets is a friend who also plays at my home group table. He assures me I'm a great DM, and the problem is "the kids," (most of the new players are mid-late teens) and not anything I'm doing wrong. He wished me luck, said he would stop by the store on event nights, but leave if the kids were there.
I wish I had a specific question to pose, but I'm just soliciting advice on how to proceed. I can provide more details about the situation if requested.
Other than the Expeditions that are 1 or 2 hours long (1-1, 2-1, 2-11, and 2-12) the Expeditions adventures are generally written to be completed in 4 or 8 hours, so doing it in one 3 hour slot is going to be a problem, even for experienced players. You might want to consider either focusing on those adventures above or consider the Starter Set or another adventure designed to be spread over several nights. As for the conflicting needs of new vs. experienced players, one way a local store I know of dealt with this was to split the table. One week they run the adventure for new players, the next week they run it for the vets. The players play half as much, but the DM is better able to address what each type of player needs.
I would do whatever you can to get that 4th hour. Heck we tend to go 5ish hours just because we tend to take forever on the 'social' pillar....
As an experienced organized play DM, the games I've run (and played) so far in D&D Expeditions have run 4 1/2 to nearly 6 hours at the gaming store. The 4 1/2 hour one was when we were trying to keep it quick, but still have fun roleplaying and accomodate new players to D&D. 3 hours is just too short- I think extra time would help more than anything.
A bunch of young-ish players may be nearly as much of a problem, maybe after a few more games they will learn to rein themselves in.
Id run it as 4 hours.. and not bother to ask for permission.
Taking an extra hour without permission is not an option (and would be disrespectful to the store owner besides), as our room is in use prior to 7PM, and the store closes at 10PM.
The idea of running one week of advanced players, and one beginner table sounds like a viable option. As long as I have the attention of a few experienced folks, a quick question regarding Escape From Phlan...
I understand that enemies do not make death saving throws, but what about healing after they've gone down? I'm studying up on Escape from Phlan, and noticed in the first encounter that Farvnik has Mass Healing Word. Let's say the PCs defeat the Hobgoblin Captain and Guard Drake. Farvnik, the Ettin and other Hobgoblin are all injured. Farvnik casts the spell. Do the first Hobgoblin and Drake get back up?
Enemies can make death saving throws if you desire (although few DMs make use of this).
Monsters and Death (PHB p198)Most DMs have a monster die the instant it drops to 0 hit points, rather than having it fall unconscious and make death saving throws. Mighty villains and special nonplayer characters are common exceptions; the DM might have them fall unconscious and follow the same rules as player characters.
DM call, though I would make the choice based on the skill of the players, level of the PCs and how much challenge they are looking for.
I think the real problem is with the veteran players who have abandoned you. Were they helping get the new players up to speed at all previously?
Just saying "You're a great DM, but ..." isn't very helpful in the long run. See if you can talk them into helping you out getting new players up and running, instead of them running off to some other venue where they are free to continue selfishly playing their game.
As an alternative, you could setup to DM at another location on a different day for the veteran players, but I wouldn't. If they aren't willing to step up and help out, why should you be inconvenienced for their sake?
As someone brand new to table-top gaming, I must say that I agree with Undrhil's comments. My first session included at least 3 brand new players (uncluding me), but there was very little help from some of the so-called veterans. I was expecting a little more help. Granted most of the veterans were 'young enough to be my kids', but I was still expecting a little more help. I almost wish that they would have put me in with a table of all veterans instead of a table with multiple new players. It was difficult for the DM to handle that many new people and at times I was lost, but I didn't want to slow the game down with all my questions to the DM. Again, I'm the new guy here, but here are a couple suggestions from that point of view:
1. Place a single new player at a table with all veterans (if you have that luxury) and have the DM set the tone that the other players help out with the 'new guy'.
2. Don't allow the new guy to create his character 15 minutes before the session starts. That's not fair to the other players. If they do not have a character of their own already prepared, then have them use a pre-gen character. Allow them to create a new character between sessions (hopefully with the volunteered help from one of the veterans). I was fortunate enough to have another DM work with me via email about a week before the session and then again about 45 minutes before the session to verify my character sheets stats/bonuses.
3. Tell the new guys to show up early (if that is an option). Have the DM (and hopefully a few veterans) use that time to explain some of the basic rules and expectations (i.e. no burning down every tavern/village that you come to, don't try to have sex with every bar maid or wench you meet, don't play this like a video game on easy level or go running into every situation with guns blazing, don't expect your player to easily dispatch anything you meet, be courteous to the other players, roleplay, roleplay, roleplay etc).
Thanks for letting the new guy comment.
Two of the vets stopped coming after the first session with new players. One lasted another session. The last, my friend at the home game, lasted three. While it's true none of them helped the new players, I neither fault them on it, nor believe it is their responsibility. As I said in the OP, Expeditions is billed as an event for advanced players. They have the rightful expectation to show up and play without new player hassles. Helping novices is one quality of a good person, but my role is to run a game, not judge personalities.
FWIW, I make my contact information available to every player at the start of each session. I have also advised the new players to learn the rules with the free PDF on their own time. I have not been contacted by any of the new players, and only one of them has demonstrated a grasp of the mechanics from session to session.
Some of the new players have participated in two adventures, and have advanced to level 3. Others are still level 2, but my plan for tonight is to obtain their consent in creating new characters based on some pre-gens I made for them, doing a crash course on the system rules and table etiquette, and to run one or two mini-adventures of Defiance in Phlan with the remaining time. Moving forward, I will be alternating T1 and T2 adventures for the new and veteran players respectively.
I didn't realize (or catch it in your OP) that there was that difference between Expeditions and Adventures, so for that I apologize. I was just trying to get across how a new player might react to his first few sessions with New vs Experienced players and what I thought would help.
Oh, and thank you for volunteering your time to DM and help out the new guys.
As a 35-year-veteran - GASP 
- of D&D, I will chime in that:
I have always / usually been willing to take a new player "under my wing" and help them get a feel for mechanics and their character's special abilities.
Sometimes to the point that I have to apologize at session's end for overshadowing them and not letting THEM play their character.
I'm also a fan of teamwork, and if I can do something with my own character to give the new guy a good chance to do his thing and shine, I'll do it. I want them to remember that they were awesome amidst the confusion, and come back again.
Update:
Got an extra hour for my table starting next week, so that will allieve a lot of the trouble. A quick review of the core mechanics and a few points on table etiquette also paid off.
An interesting learning experience for me... The first half of the session still involved a lot of me correcting them on their d20 and damage calculations. I finally said I wasn't going to correct them anymore and they needed to get used to just announcing their totals, not the straight die result. Suddenly, they were all getting it right everytime. I suspect they didn't need the mechanics primer afterall, and that they were just waiting for permission to do it themselves. That'll save a lot of time in future sessions, and I wish I had realized this earlier.
I'll still be running alternating weeks of T1/T2. I'm as eager to run T2 stuff as the vets are to play it, and the new players have a ways to go before level 5. More importantly, I'm confident DMing for the new players will be fun, rather than a chore. Thanks for your time and input, everyone.
YAY!!!!
Great to hear its working out. Good luck!