Guard and Reservists Education Improvement Act This bill revises eligibility for, and the amounts of, Department of Veterans Affairs post-9/11 educational assistance based on a service member's active duty service, excluding training. Full benefits are available for service members who serve 36 months on active duty, and tiered lesser amounts are available for service members who serve for shorter periods. The bill consolidates certain of these tiers and increases the amount of assistance for individuals who serve on active duty for: (1) at least 6 months but less than 18 months, and (2) at least 90 days but less than 6 months.