Theoretically, all state schools have to provide collective worship, not just religious ones- so unless you are able to pay for private education, it's not as simple as choosing a school to avoid this. In nondenominational schools, the majority of collective worship is supposed to be "broadly Christian" the majority of the time.
A lot of secondary schools are non-compliant with the legislation, and there certainly seems no will to enforce it. Some parents probably do have access to a primary school that doesn't carry out collective worship in practice, but this won't be all of them, and choosing a non-faith school doesn't mean you avoid collective worship.
FWIW, I don't think collective worship has much effect on children's beliefs, and it's often very light touch. However, I do think that parents should have the option to choose a school where there isn't any worship.