Reorganisation is essential if young people's skills are to match the best in the world, the LSC says.
"Independent consultants, the local LSC or rigorous self-assessment by the provider" should be used to judge the effectiveness of existing post-16 provision in areas where a reorganisation is proposed.
Supporters of small school sixth forms are worried that they could face closure because they cost more per pupil than larger further education or sixth-form colleges.
Ministers this week tabled an amendment to the education Bill intended to prevent sixth forms being closed on economic grounds. It says the LSC must show that any closure would raise standards, increase take-up rates or expand opportunities for young people.
John Bangs, assistant secretary of the NUT, warned that these criteria could still be used to close sixth forms regarded as uneconomic. He said that the guidance would "send a shiver down the spine" of those working in small sixth forms.
An LSC spokesperson stressed that private consultants would only be one voice in the process.