I never have luck with radishes, a vegetable easily grown by
3rd graders. They get leggy, but never produce nice fruit. Out of a
whole bunch that took up my (limited) space, I harvested maybe a
measely 5-6 actual radishes.
Try planting your radishes as early as you can for your growing zone.
If they're planted later when the days are longer and warmer, they
seem to have a tendency to put their energy into growing tops and
going to seed, rather than growing the root underground.