1. Playing transfers but not knowing how to get out into 3m if they have a weak hand with a long minor, and/or not understanding when it is appropriate to do so.
2. Knowing Blackwood but no other slam conventions such as cue bidding and splinters.
3. Lack of knowledge on how to bid constructively in competitive auctions and how this differs from bidding competitively to the level of the fit where you want to make life difficult for the opposition.
Here is a nice slam hand that I found virtually impossible to guide one pair through:
The auction was at 3♥ by the time I was called over and I explained to South they had underbid their hand. North proceeded to make 13 tricks and I commented that there is a better way to bid the hands but they haven't been taught it yet (I was thinking about splinters), and I was reluctant to spend a lot of time teaching them about splinters as there were two other tables that also needed occasional assistance. It is the sort of thing I would teach (amongst other things) in a slam bidding tutorial when I have time to go through it properly. In the afternoon duplicate session only two out of nine pairs found 4♥ so that would have been a joint top for them.
Here is another on at the next table:
The auction isn't the prettiest but it was the best I could do when tramlined by their very limited knowledge. 6♠ theoretically can make but it is tricky when the spades split 4-1 and the club finesse fails, it needs careful play once the bad break is discovered, declarer needs to have a trump honor in dummy and be in dummy on the second round of spades, I think running diamonds through East who holds the spades and ♦J2 brings it in, but that is very hard for a beginner to find. No-one in the afternoon session made 12 tricks, only one bid the slam and half of them didn't make game so going two down wouldn't have been a complete bottom as it happens.
Does anyone have any ideas on good ways to fill in the gaps in their knowledge without overwhelming them. Normally I pick a narrow theme, give a presentation on the fundamentals and logic then follow with practice hands. There is the odd theme where there might be some differences of opinion amongst players, for example whether new suits in response to partner's 2/3 level pre-empt is forcing or whether new suits opposite partner's overcall is forcing, but I can probably work around that.