Hi, I'll be providing some critique about your 250 box challenge. First thing first, congratulation for finishing this challenge! Give yourself a pat in the back. As for my critique:

Try not to draw on the edge of the paper, that way you can't really visualize the vanishing point. A lot of your boxes had their lines converge outside of the paper. Now, you can draw on the edge of the paper, however you will need to put your convergence point in the paper, not out.

Also, it is probably a good practice to just extend the lines from the box as far as you can until they at least converge at some point. A lot of the boxes you made only extended the lines 2x-3x times the length of the box. While it is the recommended length, a lot of your boxes seems to have VP (Vanishing points) that are too far, meaning the lines doesn't really converge after the lines were extended 2x-3x times the length of the box.

The general pattern I understand I see is that you seem to be having trouble drawing the further side of the box (back of the box). Those side seems to have largely the same size with the closer side (front side of the box). Now there are two things you need to keep in mind when drawing the further side.

*   The lines are generally smaller on the back of the box. I saw some of these on the earlier boxes and they were great. However, as you continue drawing, I saw that you made the same mistake when you first draw few drawings (around 1-50). So don't be afraid to play around instead of making the same kind of boxes, make the foreshortening a bit extreme. That way you can make mistake and learn from it.

* Now keep in mind what Uncomfortable said about the width of opposite end. That is still true, so you need to take into account that the further side of the box need to have smaller lines and at the end also looks wider. It's a bit hard to explain, but what I did was to make a really short lines on the further end, then I realised I made it too small. From there I calibrate my drawing to the next set of boxes. Maybe I'll make it too big, then I try making it small again, over and over until I managed to make the converging lines very close to each other.

Some tips that might help you when drawing the boxes is to make some sort of dot where the VP are. Then after that use a ghosting method to try to approximate the angle. Then use that ghosting method to draw the line toward the VP. It will never be 100 percent accurate, but it helped make the converging lines actually converge closer to VP.

So to sum up, try to be a bit daring with the foreshortening. While I'm not saying you should go fully extreme, a lot of the boxes have their VP too far and sometimes out of the paper. Use the ghosting method to try to approximate where the VP is. Remember that you decide where the VP is.

But overall, I'm pretty happy, you clearly show some improvement at the early part, and I think that's what the practice wants. So if you ever want to practice doing it, just keep in mind some of those tips. I wish you luck for your next lesson :D