Psh! Bad student my foot. People always want to declare themselves as being "bad", like it's going to win them cool-points from all the Drawabox rebels. Well too bad! The texture challenge was optional, so there was nothing requiring students to actually work on it at all as they went through the course. The fact that, despite picking it up after completing everything else, you still spread it out evenly across a long stretch of time, giving yourself ample time in between actively working on it (what I refer to as the "negative space" of time) for your brain to process what you were gradually learning. So you don't get to be a bad kid today. If anything, you're a student with the glasses and bow tie at the front of the class, polishing an apple for the teacher's desk.

As far as the texture challenge goes, your work is very near perfectly done, at least insofar as would be worth calling out. I mean, if I really dug deep I could probably nitpick (although that itself might be quite difficult), but all the same it wouldn't be of any actual benefit to you. I can however think of one thing to call out, which I will, in a moment.

More that, though, let's talk about why your work is so well done. Most importantly, with the majority of these you're doing a great job of leaning hard into the use of heavy blacks and heavy whites. It's not often that you hedge, and each of those bold, solid black shapes are purposefully designed, showing a lot of intent and care. That tells me that, for the most part, you're not guessing or working from any sort of randomness. Rather, you're taking what you understand of the relationships between every textural form, and every surface surrounding it, and using that specific understanding to design those shadow shapes.

Now, you may have noticed that I've used a lot of words like "mostly" and "majority" - that's because there are some cases where you aren't quite as on top of this, though the distinction is fairly minimal. This will be my main little nitpick - there are some cases where you do rely on a touch of randomness, or where you make use of the fact that if you use your pen with less pressure, or perhaps at more of an angle, it'll start to make less consistent marks, resulting in fainter lines on the page.

In terms of randomness, we can see it amongst the scratchier bits, like these, on your bread texture (number 14). Moreso, however, if we look at the "wig" texture, you end up relying on working with a lot more individual strokes - painting those shadows on one at a time. As a whole, you've still done a great job of focusing more on the spaces between the strands of hair, thus still focusing on shadows and such, but it's still important that you try as much as possible to work with shadow shapes where you first design the outline for it, then fill it in. As shown here this will allow you to achieve more dynamism, while also forcing you to just let some of your marks fall into pure white rather than trying to capture the greys in between. You can see this in this alteration of your attempt (in this example I took your wig gradient and used some photoshop magic to let it clump up a lot more).

Aside from that, honestly you've done an amazing job. You're showing incredible control of your shadow shapes, and you seem to be able to transition freely from dense to sparse and back without issue. So, it's only fair that I mark this challenge as complete.

Before I finish up, you had one last question regarding the 250 box challenge. While you certainly may submit it for official critique, I honestly don't really think there's a lot of benefit to that, or to you embarking on this additional challenge at all. Yeah, this course stresses the importance of boxes to the point of incorporating it into its branding, but they're a means to an end. If you, after having gone through the entire course, are throwing yourself back into the boxes... I can't help but ask why. What exactly are you hoping to gain from this, and why wouldn't that time be better spent on drawing other things?

The box challenge is a very simple activity, and while those new to it will benefit from having others ensure that they're employing it correctly, it is very much an exercise that grades itself (quite literally, with the line extensions and all). So, continuing to do those kinds of drawing exercises (drawing some boxes, applying line extensions, etc.) is a fine part of a warmup routine, but actually attempting to complete the challenge itself specifically, and seeing paid feedback for it seems like a waste to me.

Ultimately though, I'll leave that choice up to you. You certainly can submit it for feedback if you like, but I don't expect it will be particularly useful, or that the one critiquing it will have much to say.