Ah I see - so the problem isn't with testing, but with training the model. I think what you're saying is that only five of your students can train a model at once.
That is not a restriction enforced or applied by Machine Learning for Kids.
I assume that you have an unmanaged class.
I assume that you're using Watson API keys that you've created yourself.
I assume that you've created a single Watson Assistant instance and that you selected the Lite plan.
If those assumptions are correct, then this limit is enforced by IBM Watson. It's the limit referred to when you create the API key. (see the screenshot below). It is not a limit that I can influence.
Kind regards
Dale