PolitiFact actually has a wonderful breakdown of President Obama's Campaign Promises that are about Education. You can actually use it to not only check what he has done about education (or any other topic), but also what he has yet to do, or even what he has ultimately failed to do.

Since this question specifically asked for "contributions," here are some highlights:
Commission a study on students with disabilities and their transition to jobs or higher educationWork with schools to create more healthful environments for children
Provide affordable, high-quality child care
Recruit math and science degree graduates to the teaching profession
Address the dropout crisis by giving schools incentives for more dropout prevention
Expand teacher mentoring programs and provide incentives for more planning time
Promote innovative ways to reward good teachers
Reduce subsidies to private student lenders and protect student borrowers
Help students and their families become aware of college readiness
Expand Pell grants for low-income students
Create a community college partnership program
Expand public/private partnerships between schools and arts organizations
Create an artist corps for schools
Support increased funding for the NEA
Establish school programs to highlight space and science achievements
Encourage contests and programs to interest students in science
Increase research opportunities for college students
Hope this helps!