Ian Blott, 54, a married father of two, from Thwing near Driffield, East Yorkshire, had an "intense" two-and-a-half-year relationship with a teenager, Hull crown court heard this week.
The court was told he had sex with the girl on school premises, outside school and during trips. He pleaded guilty to four charges. The girl was 15 years old when the relationship began. The case was adjourned for the preparation of pre-sentence reports.