I looked up on Musicradio 77 website that the song "Welcome Back Kotter" was #1 on WABC's survey from May 4th, 1976. Out of the #1 song are the top 10:

2. "Right Back Where We Started From" - Maxine Nightingale
3. "Disco Lady" - Johnnie Taylor
4. "Love Hangover" - Diana Ross
5. "Bohemian Rhapsody" - Queen
6. "Boogie Fever" - The Sylvers
7. "Let Your Love Flow" - The Bellamy Brothers
8. "Silly Love Songs" - Wing (Capitol)
9. "Get Up and Boogie" (That's Right)" - Silver Convention
10. "Show Me the Way" - Peter Frampton