Each student will only have one school (their Home school), but you are correct a Home school could have multiple students.
Sample data from Unit on:
Record1 - Unit = Home Skills, Activity = Cleaning, Level = 1, Accuracy = 1, Time = 2, Help = 3
Record2 - Unit = Home Skills, Activity = Cooking, Level = 1, Accuracy = 1, Time = 1, Help = 1
Record3 - Unit = Home Skills, Activity = Cooking, Level = 2, Accuracy = 1, Time = 3, Help = 1
To get to level 5 the student would have to complete the previous 4 levels within that activity, within that unit. Are there any of your other courses available now you recommend? Besides all of them :)  - you do a great job explaining!

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Reply from Richard Rost:

If a student only has one school, then that would be a one-to-many relationship.

As far as checking to see if they have taken the pre-requisite course, you could use a DMAX function to do that. Something like:

X = DMAX("Level","SkillT","ActivityID=" & ID)

This says, "set X equal to the largest LEVEL in SkillT where the ActivityID equals 'ID'" which is a value you would send it.