Educational Radio's Identity Crisis
The Public Broadcasting Act of 1967 threw the definition of "educational broadcasting" into disarray: were Class D stations intended to be places where students of radio could learn, or were they supposed to provide an education to the listening audience? The two goals were worthy but often couldn't be accomplished together.
Some thought NPR-style educational programming provided the best public service a station could give: enlightening listeners with material commercial radio simply wouldn't program. Others thought an on-air laboratory was better, because of the opportunity it gave radio professionals of the future to hone their skills: that would make for a ready "talent pool" for the radio industry.
Some Class D stations became ardent subscribers to the national public radio theory and "professionalized" their operations. They hired full-time staff to manage and program them. The students were effectively cut out of the equation. Many of these operations also upped their wattage, shedding their Class D license status in the process.
The vast remainder of Class D stations remained student-run, programming what those students in the studio wanted to hear. On-air mistakes were common, and while professionalism was often absent, it didn't mean the programming suffered: the on-air liberty afforded to students in such operations often made for innovative broadcasts.
It is the spirit of the Class D radio laboratory-type station which fueled the renaissance of college radio in the late 1980s and early 1990s - when "alternative" music began its rise in popularity and forced change in the recording industry. Non-NPR non-commercial educational stations were the ones breaking new acts - and as soon as record labels recognized that fact, they jumped in head-first. It was the handful of Class D stations still on the air that often led the way.
By this time, though, LPFM in America had all but been outlawed.
Class D Licenses Disappear
The Corporation for Public Broadcasting completely abandoned the "radio laboratory" idea in 1972. That year, CPB filed a petition with the FCC to effectively standardize educational radio in the United States along the national public radio model.
In its petition, the CPB challenged the legality of those student-run stations that still existed - claiming they didn't effectively serve the public interest because their programming was so variable in quality and quantity. Student-run stations often shut down during school breaks and vacations, and often ran limited operating hours when school was in session.
The CPB saw this as a waste of radio space, as these small part-time stations were taking up parts of the spectrum where higher-power "public radio" might otherwise be available.
The FCC apparently agreed, and decided to phase out the Class D license in 1978. Those Class Ds that did not upgrade their power above 100 watts were kicked out of the 88-92 MHz part of the FM band. Class D operations that couldn't find space in the commercial segment of the spectrum (93-108 MHz) were forced off the air.
Not all Class Ds were killed off, though - some still exist to this day (including my old college radio station, still on the air with 36 watts just outside the Chicago metro area).