Assessing projects

Now that the last day of school is here, it's finally time for me to grade students' final projects, and I'm realizing that this is really hard for me. For Algebra 1, students had quite a few options to choose from, of varying difficulty and mathematical content.

Some students worked on the same project for a week, while others worked on two or three during that time. Some created a product (video, book, poster), while others explained their process verbally to the class and/or annotated their work on paper.

I feel that this year more than in the past, students engaged fully with their projects, worked productively, and accomplished something meaningful in the last week of school, but I have no idea how to fairly grade this work. Should a weaker student who picked a project that was challenging for them and put a lot of effort into it be graded lower than a stronger student who completed a more challenging project with perhaps less effort? What about a kid who tends to be easily frustrated, but worked through his sticking points and got himself through areas of frustration? I'm not even sure that I can quantify their effort... some students chose to do extra work outside of class (this was discouraged, but not banned), while others didn't. Some volunteered their time to help their peers while others preferred to work alone. How can I tell how hard a student is actually working? And should it matter in assessing a project or do I grade on mathematical content alone? I do have a rubric (attached to an earlier post), so that will help somewhat, but I'm still mulling over if each category should be referenced to some norm (what I think an Algebra 1 student should be doing) or compared to that particular student's previous progress and how much they learned doing this project. I would love to hear from others who have thoughts on how to assess projects.

P.S. All of the photos are so boy-heavy because this class literally has 3 girls in it. Did I mention that it's also the last class of the day? Sigh.