Flight schools that operate under Part 141 of the FARs are strictly regulated by FAA, their flight and ground school courses must be FAA-approved. Students who learn better in a structured climate will choose a Part 141 school.
Instructors at a Part 61 school should operate from a syllabus, just as a Part 141 school, but they are not required to do so. Ground school is not required at a Part 61 school. If your life and work schedule do not fit into a relatively strict training regime, Part 61 is for you.
The airplanes and instructors at both types of school must meet the same standards.