Math skills are like a sport, they take time to master, but you can get there even without superstar skills (there are some people who have math issues … but for a child who can say understand algebra, it is best to just do lots of problems).
Many of the top math students have been doing extra problem sets for years, so they are basically like the kid who has been shooting hoops on the driveway for years. They are right now better than you, but if you practice, you can get to JV level and even beyond.
Memorization is a skill. Reading is a skill. Writing is a skill. All need practice and improve with time.
It may still be good to try to figure out exactly what your child is struggling with, so you can make sure they have no underlying issues (reading difficulties through learning disabilities) and can work on improving the skills that they are weak in. And there are for example, speed reading classes. Or math tutors to help fill in gaps in understanding or just work through enough say algebra problems that they can do the manipulations correctly. Reading is sort of done alone … but say reading a book and writing a good critical essay, that takes practice. Effort on one assignment can yield improvements in many assignments in the future.
Study habits can also range from stellar (kid sits down with total 100% focus, reads material, reads the assignment carefully and completely, kid pumps out the homework set, kid goes outside to shoot hoops) to dreadful (kid sits down and is distracted for 50 minutes, does not read instructions, 4 hours later is still sitting there … etc). If appropriate, maybe you can watch their habits and see if you can improve them, sometimes even a better desk area can help or a better incentive (finish that up, let me read it to make sure it is A work, then we can go to a movie or whatever).
Life is filled with lots of things that you can get better at if you choose to try: ice skating, skiing, tennis, crossword puzzles, video games … but really there is no shortcut for just putting in the effort.
There are some really brilliant people out there, and there are some people who are born to be theoretical physicists or mathematicians for whom everything they learn from age 5 clicks perfectly into place. But honestly, most of the world is just people who focus and work hard … preferably on something they have some skills and aptitude for and … more importantly … something they really love. High school is a good time to find that love … and make sure you are competent in all the other necessary life skills.
While it is nice to think that kids should be self motivating, some of the tiger parenting is just making your kids do a lot of work … and for some people, this really does get them somewhere.