Trimmer with no attachment, every 2 weeks 
I shaved my head from about 13 to 17. Tight fades or shaved for next 20 years. Still today.
Used to cause I hung around gangster types. 
Yep, I did it with a razor then got sunburnt real bad and my head started peeling at the same time my hair was growing back.
It looked like there was an earthquake on my head.
Once a week. With a butter knife