Regardless of how you grade math tests, the amount of work is the same. However, the speed at which you grade is changeable. The key lies in freeing up your working memory to focus on a single task at a time. If you want to grade math tests quickly, you must do so in a way that conserves your working memory.

Create the answer key for the problems. Make sure that you have clarified which parts of each problem are needed for students to obtain points. Only if this is clear can you know what to look for in each problem. As adding is more simple than subtracting, it is best that you assume each problem starts out at zero points and then give points rather than assume each problem starts out at full points and then take away points.

Divide the problems into sections. You should be able to know on what each problem was testing the students. Draw horizontal lines on your answer sheet to divide up the problems into distinct sections. If the test was only testing students on one concept, then consider the whole test to be one section.

Grade the first section for one student. Grade the first section according to the criteria on the answer key. Do not worry about this student's other sections for now; you want to free up as much working memory as possible.

Add up the points for this section. Put a total score for the first section on the student's first section in a clear place.

Repeat for all other students. Go through the pile of math tests, grading the first section and giving it a sum for each student's paper.

Repeat this process for the other sections. Go through the pile again as many times as it requires you to grade all sections.

Sum up the section sums. Add up the section sums of each paper to get each paper's total score. You are done.
References
 "The Cognitive Neuroscience of Working Memory"; Osaka, Logie, D'Esposito; 2007
 "Handbook of Classroom Assessment"; Gary Phye; 1997
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