Duncombe School was founded in Pegs Lane, Hertford in 1939 by Miss Lily Taylor with just eight children on the roll. The number of pupils increased steadily as a reputation for excellence spread, necessitating the move to larger premises in Westfield Road, Bengeo a few years later and to the present site in 1951. Duncombe has continued to flourish and there are now over three hundred boys and girls aged between 2 and 11 years at the school.

Situated one mile north of Hertford town centre, in four and a half acres of grounds with magnificent trees which are visible from both Hertford and Ware, the Main School (5 - 11 years) occupies a Palladian-style mansion dating from the 1860s. The house was built by Mr Jasper Gripper whose great-grandsons were among the first pupils. Classes of around eighteen study either in the mansion, where the large rooms and floor to ceiling windows make the classrooms airy and light, or in the later modern wing built to a complementary design.

'Treetops' is home to the pre-prep (2 - 5 years) and is a purpose-built early years facility within Duncombe's grounds. Treetops opened in 1998 and takes its name from the school's semi-rural location at the top of Port Hill, overlooking the trees of Hartham Common.

In its two most recent Ofsted inspection reports (2005 and 2008), Treetops was declared ‘Outstanding' in all areas.