We had a chance to work through some of the lessons. Overall very solid foundation I would say. My son's critique was that it was a little confusing when it came to answer format and that he felt the lessons kind of jumped around. Other than that he found it 'OK'. He's 10 so that means you didn't mess up too bad. lol.
We did have a few issues.
1. The hint on the equation simplification section describes the format of the simplified equation as 6 x l. (actual number varies 2 x l x 3) But the only answer that is accepted is in the format is 6l, sans the 'x'.
2. I found the hints' font coloring very hard to read on my old eyes. Also, we did not find out the desired input methods until fairly far along. The SHIFT-8 etc was new to my son and kind of obscure given how soft the font was. Maybe a heads up of the conventions at the beginning?
3. In the word questions section, sometimes the amount being compared to determine the total amount of cages vs squirrels was the exact same. Actual examples -> 2 cages and 2 squirrels vs 2 cages and 2 squirrels. I assuming the desired question would have compared 2 cages and 3 squirrels vs 3 cages and 2 squirrels. (Although that doesn't make sense either.)
4. The spoken word button is a great idea, but the voice is almost incomprehensible to a 10 year old. I know you didn't create the voice, but if there is another easier to understand voice that would help.
5. My son was initially confused by going some distance in a negative amount as a representation for reverse.
6. My son is very competitive and he enjoyed the speed challenge, but there was no reward or signification of accomplishment at the end of the challenge. He wanted to know how well he did.
6. There are some minor grammar errors.
My impression was that the layout and design was on par with other online offerings that we use daily. I actually liked the lower distraction level. The site and UX were predictable, easy to use and did not add to the stress level of the student. I'll have him do some more over the next few days. Keep up the good work!