As promised, I shall now dwell on the business of chess improvement based on my experience.
Most players, weak or strong, fear and respect the endgame respectively. Unlike opening variations where one can devote time to learn 'tricks' to catch the opponent off-guard to snare a piece, a queen or even mate, the endgame does not reward the student in this manner.
I agree with Andy Soltis when he says the chief phobia about endgames is chiefly caused by the chess authors way of presenting the subject. Tons of exact endgames knowledge (where if you know the moves you can win) in the form of encyclopedic information about how if your pieces lie within the zone you win, if not you draw, or who wins if he has the move etc. Too much of such information is utterly useless as the when the time does come to apply such information over the board, much of it would have been forgotten.
On the other hand, there's the other area of practical endgame strategems such as the fortress, creating 2 weaknessess, widening the beachead, centralising the King etc that would need to be understood before one can conduct a decent endgame.
So with limted time on our hands, how should one go about apportioning time for the endgame? It depends greatly on the level of the player. The stronger the player, the more emphasis on knowing theoretical endgames and less on strategy. As for the primary school chess player at school level, learning 30 theoretical endgames and knowing about the 10 main strategems should suffice.
Where to get this knowledge? Of course, coaches will know where but for those who do not have them, the internet is abound with such information. What I would do is list the necessary endgames for the student to go do reasearch on.
EXACT ENDGAMES :
1 Checkmate with K and Q vs K
2 Checkmate with K and R vs K
3 Checkmate with 2Bs vs K
5 Key Squares
6 Square of the Pawn
7 Floating Square rule
10 Outside and protected passed pawns
Pieces (and K) vs Pawn (and K)
11 Q vs b,d,e,g pawn on 2nd or 7th rank
12 Q vs a,b,c,f pawn on 7th rank
13 R vs P on 4th, 5th rank pawn
14 R and a,h pawn vs R
15 R and b,c,f,g P vs R
16 R and a,h pawn after 5 rank
17 R and b,c,f,g pawn after 5 rank
18 R and central pawn d,e vs R
19 Lucena's position
20 Philidor's position
21 Back rank defence
22 Short side for K, long side for R
23 Using pawn as Shelter for the King
24 Checking distance
25 Rooks behind passed pawns
26 Active Rook and its importance
Bishop vs Knight ending
27 B and pawn vs N
28 N and pawn vs B
29 Good N vs Bad B
30 B vs N and pawns on both sides
1 Centralise the King
2 Activate pieces
3 Pawn structure and weaknesses to avoid - isolated, doubled,pawn islands
4 Principle of 2 weaknesses
5 Creating a passed pawn
6 Playing with the whole army
7 Widening the beachead
9 Creating pawn weaknesses by attacking pawns
10 Gaining critical tempo (esp in pawn endgames)