Kindergarten Plus Act of 2008 - Authorizes the Secretary of Education to award competitive grants to states to provide Kindergarten Plus (K+) programs of voluntary full days of kindergarten during the summer before and the summer after their traditional kindergarten school year.
Directs the Secretary to ensure, to the extent possible, that each grant is of sufficient size to enable the state to provide K+ to all eligible students served by the local educational agencies (LEAs) within the state with the highest concentrations of eligible students. Makes children eligible to participate in such programs if they are: (1) five-years old or will be eligible to attend kindergarten at the beginning of the next school year; (2) from a family with an income at or below 185% of the poverty line; and (3) not already served by a high-quality program in the summer before or the summer after the child enters kindergarten.
Requires states, in awarding subgrants, to give priority to LEAs that: (1) serve the greatest number or percentage of eligible students; and (2) propose to reduce class size and student-to-teacher ratios in K+ significantly below the average ratios in regular kindergarten classes served by the LEA. Provides for direct grants to LEAs whose states do not apply for grants. Sets forth K+ teacher and personnel quality standards.