I and my kids also have dyscalculia and I found Math-U-See and ALEKS to be helpful.
They still did not love it but they did make progress.
Math-U-SEE makes an effort to teach why and how the formulas work, so that you do not need to rely as much on your memory. My Youngest started out in public school with an IEP and made no progress in math the first two years. I was homeschooling his older siblings and using Math-U-See. I introduced it to his special ed teacher and ended up converting them. They started using it for all the kids with math issues in their IEPs.
My two children that used ALEKS in highschool would complain that they were not learning anything, it was too easy. In fact they were, but the nature of the software is to present the new material as you show readiness. They did not feel the same struggle they were used to feeling with Math concepts. Possibly also it forced them to go slower than they would have liked to. I’m not sure. In any case they learned the material.
If money is an issue or being constrained by someone else’s time table is, then try Kahn Academy. It is free, online and video based. My son used it when in college as an aid to understand concepts in his math classes. I would suggest getting an SAT practice book and use that as the base and watching the videos related to the subject. The practice books do a good job condensing highschool math into a smaller package and it actually covers more than the GRE. This can help IF your son gets overwhelmed by the volume of info your son sees in a textbook.
Dyscalculia.org has a couple of free tuturials on learning how to learn towards the bottom of the page.
And a note of encouragement in case you don’t have personal or extended family experience with dyscalculia. It does absolutely make school/academic math very difficult and tests a nightmare. It can be very frustrating because you may be able to conceptualize the math problem but can’t get the right answers because of ridiculous things like transposition & alignment on the page.
However, it does not have as much as an impact in the workplace. You can keep relevant formulas posted on the wall of your workspace and use excel to plug in the formula once and keep everything nicely lined up with minimal effort. And it does not need to prevent one from getting into career of high interest that have a math basis. It does mean if there is a gateway issue, ie a math test to get into the program or a passing grade in a math class to graduate…then you may have to make a few attempts or you may have to get really creative and find a back door. These days it is a little easier because colleges/universities do have disability centers where you can request accomodations.
Examples of successful math involved careers, not everyone has or wanted one, in my dyscalcula ridden family: research scientist; energy services business owner; video game art & programmer (very back door strategy because he couldn’t pass the math test to get into the programmer path); NICU nurse; and financial controller. Now it is not that the dyscalculia went away, you just have more ability to make adjustments for oneself outside of an academic program. And these people from the last generation that were not homeschooled were abysmal students until college and usually did not go to college immediately after highschool. Time, scheduling, calendars, prioritizing are all still challenging.