I do get what you're saying, but the 250 box challenge is intended to be a focused period of - well, not grinding, because it has a clear end point, but focused exercise so that when students continue onto Lesson 2 and beyond, they've had a solid chance to kick their comfort level with the basic principles of spatial reasoning forward. As with the lessons, the challenges are included at specific points where they are the most effective.

As you stated yourself, the 50% rule is indeed the best thing to mix it up with - it's both there for the intrinsic value it offers for the learning experience, but also to break up the monotony.

That said, I will consult with one of my teaching assistants/illustrators who has gone through this course with ADHD and get her further opinions, as she comes in with the additional experience of having nearly finished the course (and thus can understand where the different lessons/challenges integrate into it) and has done so both with medication and without.