If you are currently enrolled in a student health plan, you can still qualify for Marketplace coverage and subsidies if you apply during open enrollment. During open enrollment, you can sign up for a Marketplace plan and you may also qualify for premium tax credits, depending on your income. You will have to drop your student health coverage before your Marketplace plan becomes effective in order to be eligible for premium tax credits.
Outside of open enrollment, you cannot voluntarily drop your student health plan coverage in order to qualify for coverage and premium tax credits. However, if you involuntarily lose eligibility for student health plan coverage mid-year—for example, if you drop out of school and so lose eligibility for the student health plan—you will qualify for a special enrollment period and be able to apply for Marketplace coverage and premium tax credits. The special enrollment opportunity will last 60 days (although there may be an extension for exceptional circumstances), so be sure to contact the Marketplace promptly to notify them of your qualifying event. (45 C.F.R. §§ 155.410, 155.420).