Hi fish nutter
The way the bacteria works is that it will eliminate the same amount of fish wastes in your tank as it did in the tank it was removed from. For an example, if your teacher has a enough media to support 20 guppies and gives you 1/2 of it, you can immediately keep 10 guppies or about the same amount (size-wise) of other small fish. If he gives you 1/4 of it, it will enable you to safely keep 5 of them or the equivalent. Be sure to get it into your tank as quickly as possible.
It would probably be safest to tell him what you have and ask him to estimate how many fish whatever he gives you should support. Then you will know a rough estimate of what to expect. It would be better to start slow and wait to add more fish until you are sure your tank is cycled fully with what you have. Then the bacteria will be able to reproduce quickly when you do add new fish.