Teaching unions have generally negotiated better-than-average natal leave policies and decent health insurance. With a small amount of planning and foresight, it would be possible to get pregnant such that the baby is born in the spring, and the post-natal leave extends to the summer break, effectively extending the leave period by an additional 2-3 months.
Teaching tends to not have a lot of cut-throat career advancement, compared to some other professions. Mostly, you get salary increases based on seniority and years of service, or one-off boosts, like completing a master's program.
Being a female-dominated profession, where the bulk of the other employees have been, are, or are planning on being mothers, there's likely more understanding and acceptance of child-related absences. Also comparatively generous sick-time policies.
Completely unsubstantiated, but people that choose to spend the bulk of their working hours with children might be more favorably disposed to them in general than people who choose other occupations.