For nine months, from 1928 to 1929, Johnson paused his studies to teach Mexican–American children at the segregated Welhausen School in Cotulla, some 90 miles (140 km) south of San Antonio in La Salle County. The job helped him to save money to complete his education, and he graduated in 1930 with a Bachelor of Science degree in history and his certificate of qualification as a high school teacher.[29][30] He briefly taught at Pearsall High School before taking a position as teacher of public speaking at Sam Houston High School in Houston.[31]
When he returned to San Marcos in 1965, after signing the Higher Education Act of 1965, Johnson reminisced:

.mw-parser-output .templatequote{overflow:hidden;margin:1em 0;padding:0 40px}.mw-parser-output .templatequote .templatequotecite{line-height:1.5em;text-align:left;padding-left:1.6em;margin-top:0}I shall never forget the faces of the boys and the girls in that little Welhausen Mexican School, and I remember even yet the pain of realizing and knowing then that college was closed to practically every one of those children because they were too poor. And I think it was then that I made up my mind that this nation could never rest while the door to knowledge remained closed to any American.