Yes - schools invariably can use additional help, in class, the office, playground or dinner hall etc!
I started as a parent helper, hearing readers, and went on to do gardening activities with Yr6, and ran an after-school Keyboard club for informal music. I then became a TA in a different school, for ten years, and two years in a tough comprehensive. When I retired, I carried on voluntary help in schools. One of my earliest 'readers' turned up in another school, SEVENTEEN years later, when she was in her final year of Teacher Training; our roles were reversed, and SHE needed to direct ME in the classroom!
And if you have any special skills - music, drama, art, sport, ICT -you can be even more useful.
It can be enjoyable, though sometimes frustrating, and some children can be more relaxed with a 'voluntary' helper than with teacher or TA.
Don't be shy about what others may think, and don't be afraid to 'sell' yourself if you do have particular skills.