The GI Bill (Serviceman's Readjustment Act of 1944) did not directly boost the U.S. economy after the war, but it did set aside thirteen million dollars for
education, vocational training, and medical treatment for Veterans
This provided the opportunity for returning soldiers to receive a college education at government expense. It also provided financial assistance for them while they were enrolled in college. The end result was that many more young men enrolled in college than had previously been the case. As a result, a more educated, highly trained workforce developed in the years after the war. This in turn led to increased production and a boost to the economy.
A more direct effect on the economy was the demand which had built up for automobiles and other big ticket items which had not been produced during the war years. This increased demand led to increased production and provided the most immediate boost to the economy.