There are a lot of students who seem to be unable to retain math procedures in spite of herculean efforts to do so. In particular, some people on the autism spectrum can seem to have a wholly divergent comprehension and mental "filing" system, making connections that other students don't make, and finding the associations which enable other students to retain their learning completely ineffective or incomprehensible. I'd love to hear from anyone who has a deeper understanding of what is happening for these students! In the meantime, my pragmatic-tutor mode has led me to rely on creating math journals with such students, and advocating for their use in all math work, including assessments!
It can take some careful conversation with some math teachers, but eventually most can understand: this student can work endlessly to comprehend and complete various math skills exercises and activities—perhaps several times as much practice as the average peer who retains the skills mentally—and it just does not stick, in much the way that spellings do not stick for dyslexic students, so they have to re-spell almost every word, each time they write it, even on the same page. The parallel breaks down with math, in that a student cannot usually "sound out" the procedure for a math problem the way one can sound out a word. So what would an adult do in a professional situation in which the requirements to produce work outstripped the capacity of their memory? Write down the things they need to remember! Thus, this student has created a journal of math procedures. This is in no way an "easier" way to do math: they have worked harder than the vast majority of peers just trying to retain all this math mentally before realizing a journal was necessary, and then they had to meticulously re-learn the procedures yet again and write them down in an organized manner that could be used as a reference. And of course, the journal does not contain answers, it contains procedures, and therefore still requires the critical thinking needed to choose the procedure, and the attention to accurate application and calculation required to answer the specific problem presented to them. Thus, for this student, it is appropriate and fair for them to use the journal for all math work, including assessments. In fact, it would be unfair for them to be deprived of it.
We put one problem type per page, with a heading at the top that uses words the student will recognize when it counts. Similarly, we don't worry particularly about neatness, but we simply employ the journal later, and if it is not useful because it is not legible, we fix it.
I recommend using a small, loose-leaf binder, so that the student can alphabetize the pages for easy access. Ultimately, though, we have to use what the student is comfortable with and agreeable to using... or they won't use it anyway!