Final answer:
The main idea in paragraph 4 is that giving parents the ability to choose the schools their children attend creates more options for low-income families.
Step-by-step explanation:
The main idea in paragraph 4 of the passage is that giving parents the ability to choose the schools their children attend creates more options for low-income families. It states that school vouchers and charter schools are part of the concept of 'school choice' and argues that more choices can improve educational outcomes. While the effectiveness of school choice can be debated, the author suggests that it provides an opportunity for low-income families to have access to better education.