"When one player has four of the same cards of a given rank, they form a book, and the cards are placed face up on the table. Four cards is always a match, never two."

 

So I think you should have four of each. Hope this helps!

 

I use four cards to a set but allow the children to put down when they have 3.  The fourth card can now be put down anytime and counts as a point for the owner. The game goes quicker this way.  Traditional Go Fish! is just too slow for most classroom situations, so be careful to keep the number of players to a group to 6 or below otherwise you may get bored and troublesome students.

 

David