My favorite feature of QuizNinja is the mathematical grading aspect. Flubaroo is an awesome resource to grade form responses, check it out! However, it is impossible to add in all of the options that are mathematically equivalent. QuizNinja does a much better job of validating mathematical responses.
Once you have created forms using QuizNinja, you grade the student responses.
Click on QuizNinja->Grade individualized forms to open up the sidebar.
When you grade the responses, you can also choose to send an email to the student containing the step-by-step solutions for the problems they answered incorrectly. If you do not want to send the email, choose No from the dropdown box.
Once you have filled in the Email Subject and body, if you choose to send emails, click Grade responses.
QuizNinja will pull each response and check it against the correct answer. It validates them mathematically so if the student responds with 16x/(4x) and the correct answer is 4x, it will be marked correct. There are some quirks of order of operations that QuizNinja misses, so please double check to make sure problems that are marked incorrect are actually incorrect. I understand this is not ideal, but I feel it is much better than previous solutions.
If the answer is correct, it will change the background color to Green and if it is Incorrect it will change the background color to Red. It will also sum up the correct number of problems and put the total in the penultimate cell to the right on that row. For each incorrect problem, QuizNinja will send the step-by-step solution in an email to the student if you choose that option, otherwise no email will be sent and the results will stay contained in your spreadsheet. I like the color coding option because I can quickly scan to see how the class did overall on the assignment. Finally, the Form Created cell will turn light green when the student's quiz is graded. This is a quick way to see which forms do not have a response yet.
Below is a sample email showing the step-by-step solutions to the problems they missed (in this case it is Student 5 from the pictures above, who missed #1 and #3).