First, each Mahjong set contains the following 146 pieces:
4 each of Bamboo tiles numbered 1-9 (e.g., 4 Bamboos with a 1, 4 Bamboos with a 2, etc.)
4 each of Wheel tiles numbered 1-9
4 each of Wan tiles numbered 1-9
4 each of Wind tiles labeled E, W, S, and N (e.g., 4 East, 4 West, etc.)
4 each of Dragon tiles labeled C, F, and P
1 each of Flower tiles numbered 1-4
1 each of Season tile numbered 1-4
2 extra tiles
Second, a standard playing deck includes 52 cards. Many include 2 jokers.
A very simple strategy that is hinted at in the original question:
Use playing cards to create the board. Use Mahjong tiles as the pieces
12 standard decks of cards results in 324 cards of each color, and 648 total cards
2 standard Mahjong sets results in 146 tiles of each color (counting the 2 extras in each set
Assigning one card per board square results in a maximum of 10 completed chessboards (648/64)
Assigning one Mahjong card per chess piece results in a maximum of 9 completed sets of pieces (146/16)
Now, a system is needed to represent chess pieces with Mahjong tiles. This does not necessarily have to be uniform across all 9 sets
Pawns can simply be the backsides of Mahjong tiles. Thus, they can be any of the 146 tiles
Each Mahjong set (dark and light) must be broken into 9 16-piece sets of chess pieces, 8 of which are pawns
This leaves 9 queens, 9 kings, 18 knights, 18 bishops, and 18 rooks
Designate 9 of 16 Wind tiles as queens
Designate 9 of 12 Dragon tiles as kings
Designate 18 of 36 Wheel tiles as knights
Designate 18 of 36 Bamboo tiles as bishops
Designate the 18 of 36 Wan tiles as rooks
Repeated for each Mahjong set, this allows for some sense of uniformity between the 9 chess sets
This appears to be the maximum number of sets unless the schoolmaster is not too attached to his playing cards
If he is not, you should quarter each card, resulting in 2496 cards
Using 1152, we could construct 18 chess boards. These can be any card, regardless of face value
Because each card typically has two identifying symbols (one on the top left and one on the bottom right), we have 96 card pieces of each card number (including royal ace, king, queen, and jack)
Designate 18 kings as chess kings
Designate 18 queens as chess queens
Designate 36 aces as rooks
Designate 36 jacks as bishops
Designate 36 tens as knights
Designate 144 quarter-cards without a symbol as pawns
Cards could be bent slightly in the half and placed as an upside-down V in order to assist in visibility and movement
For each chess game, one side plays with cards and one side plays with Mahjong tiles
This allows for 18 games of chess and accounts for every student
In reality, the remaining pieces might be used to construct additional boards, but that seems unnecessary