Are you arguing for or against charter schools? Charter schools are a very broad category. Some are great, and some are terrible. You can use examples of specific charter schools that are doing well. If you are arguing against them, I would focus on the fact that there are not many similarities.
If you want to argue that charter schools are not good, you might have a thesis statement like this:
Charter schools have a negative effect on public education because they siphon off funding from regular public schools, because they are in many ways beyond the control of the public school district, and because the results they achieve in learning are often no better, and sometimes worse, than the results achieved in regular public schools.
So, are you asking about a good thesis for an argumentative essay about charter schools? If so, you have to base this largely on what you believe. If you believe charter schools are good, a good thesis might be something like "Charter schools have the potential to improve the school system by forcing the regular public schools to compete for students."
Mmmm....Here's one: "Charter Schools are a mistake. The education system should instead aim for complete equality between schools in terms of resources and quality of learning, teaching, etc. Additionally, complete equality in society should be fulfilled so that there are no differences in the quality of education anyone aquires."
Can any one Help me.