Starting with the form intersections and cylinders in boxes, you really knocked these out of the park. I'm especially pleased with the spatial reasoning skills you're demonstrating there with the intersections. You're demonstrating a level of comfort with manipulating those forms and determining how they'd cut into one another that suggests a great deal of growth over the course of the lessons. Very well done.

Moving onto your vehicle constructions, I think you've achieved a great deal across the board, although there was definitely a good deal of struggling along the way. This is, of course, normal. This lesson is exceptionally difficult, and the cars especially (which were the primary focus of your difficulties) are considered the "boss fight" of Drawabox for a good reason.

One thing that did stand out quite a bit was that you only appeared to take fairly limited advantage of the permission to use a ruler, ellipse guide, ballpoint pen, etc. Instead from what I can see, it looks like you used those tools when creating an underlying breakdown, and then went back on top of them with a fineliner for a freehand "clean-up pass". I'm not sure why you did this, but it was specifically mentioned that you should not at the beginning of the lesson:

Ballpoint pen for your linework (don't switch pens to do any sort of "clean-up" pass - use the same pen through all your lines, including construction/box subdivision/etc)

Imposing further difficulties like doing the 'final drawing' freehand aren't really going to serve you particularly well as far as learning what the lesson is conveying to you goes. If you're allowed to use certain tools to make things easier, do so. The purpose is to make the actual execution of the marks easier so it doesn't further expend your cognitive capacity, which should otherwise be focused on where the lines should be going.

Also, when you do go over lines that have already been established (to add line weight for example), don't trace over it slowly and carefully. "Tracing" as an approach is something that focuses entirely on how a line exists on the page, and ignores how it moves as an edge through 3D space. I can see a good deal of that early on, where many of the darker lines of your cab-over truck appear to waver and wobble quite a bit. This in turn undermines the solidity of the resulting form.

Another point I did want to mention was that your solid black areas should be reserved almost exclusively for surfaces that receive cast shadows. The only exception would probably be the interior of the vehicle, when seen from outside. In your cab-over truck, you used the solid black shapes to colour in the windows, and also to apply what effectively is form shading to the wheels. Remember that cast shadows are specifically where a form casts a shadow onto the surface of another form. If the form in question is the one being filled in, then you're confusing it with form shading, which as explained back in Lesson 2 should not be included in these lessons' drawings. This diagram can help you distinguish the difference between form shading (on the left) and cast shadows (on the right).

Looking at a lot of your later drawings, I think that what gets most in the way is a matter of patience. The cars especially are extremely time consuming. Even when drawing the mustang demo myself - and I understandably have a good deal of experience already - it took me upwards of two hours to complete the whole thing. Often times when students feel something is taking too long, they'll start skipping steps. They'll observe their reference a little less carefully. They'll avoid features and details that could be constructed, but would end up demanding even more of them. And as a result, the cars come out feeling somewhat half-baked.

Now, I still believe that what impacted your cars most negatively was the need to freehand-trace everything for whatever reason - and as I said before, that was a bad call. I'm seeing fairly limited use of the ghosting method in those freehanded lines (a lot of lines that waver quite a bit, and a number of places where you've got back over them multiple times). But as far as the proportions go, those were determined ahead of time with the subdivisions and such you'd laid out. What I'm not seeing on your pages however - though they may well simply not have been included in this submission - are the kinds of orthographic proportional studies you see in the camaro demo. I also do something similar with the mustang demo, though more directly on top of my reference image.

Taking the time to pin down the specific proportions is quite important. Another element that you may want to try in the future is pushing the vanishing points a little farther away to make the foreshortening somewhat less dramatic, and lead to less distortion overall. And lastly, of course, taking more time to study your reference more carefully, and making a point to continually look back at your reference over and over is critical. There are a lot of really deviations between your reference and your drawings that you've missed. It's understandable, as you're being faced with a lot of visual information here, but the only way to approach that is to steady your mind, and to really take your time. The drawings in this last lesson can legitimately take several hours each, so don't be afraid to really invest your time. You can even split them up over multiple sittings if necessary.

It is worth mentioning that while the back of the mustang you drew got really stretched out, I feel the construction of the front with its headlights, grill, hood, etc. was really well done. The sense of solidity there is remarkable.

So, here's what I'd like you to do. I'd like to see 2 drawings of cars. One of them should be an old style car like a model T or something similar like this one, but make sure you get a much higher resolution image to work from. The other one can be something of your choosing.

Do not trace over your lines freehand. Use rulers, ellipse guides, etc. wherever possible so you can focus purely on where the lines need to go instead of whether or not you can get them there on your own. And of course, try to identify the proper proportions of your cars beforehand. Use multiple reference images if necessary to give yourself all the information you need.

Also, set the fineliners/brush pens aside. Use only a ballpoint pen. And of course, take your time. Based on when you submitted your wheel challenge work (May 1st), you've barely given yourself two full weeks to complete this lesson. Given just how much time each individual drawing can take, in combination with the 50% rule from Lesson 0, I find it hard to imagine you gave each drawing as much time as you could have.