When it opened, Dinnington High School served 1,633 pupils from a catchment area consisting of Anston, Dinnington, Lindrick (the West Riding portion thereof), Woodsetts, Firbeck, Letwell, Harthill, Kiveton, Thorpe Salvin and Wales, with some students also coming in from Thurcroft and Maltby. Roger Whitfield adds: "some of my mates came from further out that way, Thrybergh and Sunnyside." It was a large catchment area that required a large school. But planned second and third phases of extension would be abandoned when it was decided that a new Rother Valley South school would be built for 1967/8, taking away half of Dinnington's catchment area. This was a mixed blessing for Dinnington, especially in the years before Wales High School opened, when most pleas for further campus development would be quashed on the grounds that half the catchment would soon have new digs. As it was, things didn't quite work out that way. It's true that Dinnington's school population has gone down since 1963, but only by about 150 pupils. Population growth thanks to the establishment of the Commuter Belt has meant that for most of its lifetime Dinnington has been stuck with more pupils than it was made to hold.

The Wales plan essentially put paid to Phases II & III of the DHS campus, and everything from this point on took even more fighting for than usual. Wales High School finally arrived in 1970, three years later than anticipated, but even in 1966 (a year before Wales was supposed to arrive), DHS was so desperate as to be reconsidering a return to Throapham Manor. The place had never been much good as classrooms, but could at least be put to use as a Remedial retreat.

By this point there were twenty temporary classrooms on campus: the 12 Terrapin rooms, the 4 West Riding rooms, and, presumably, the two longer Terrapins at the back of the Terrapin Plateau.

This was still insufficient, and so the hire of two more double classroom units was requested for 1967. It seems that these eventually arrived for the start of 1969, in the form of two West Riding blocks; one from Todwick C of E Primary, and the other from Garforth Old Secondary School. These are presumably what became known as the Tennis Court Buildings. 

Further respite came in the form of a ROSLA (Rising Of School Leaving Age) Unit of four classrooms, to cater for 180 pupils and to also arrive in September 1968. This building was dubbed the Turret, and would rehouse the 6th Formers (becoming the New Sixth Form Base). The money for this seems to have been a standard grant to coincide with the change in school leaving age policy that was due in 1972, but the school also managed to get £15,000 out of the LEA to build two Technology workshops, to allow the school to stop borrowing the workshops at the Tech. This plan was expanded to three workshops and the Technology Block was born. The Tech Block and the Turret were built by Pace Construction at a cost of £45,564.

There was also a moveable Housecraft room on campus at this time. This seems not to have lasted into the 1990s.

Despite a seeming surfeit of halls and gyms, there was such a high roll call of exam students that the Lyric Theatre had to be borrowed as an exam venue in the late '60s.

Through the next fifteen years the area to the north of campus was further developed. In April 1969, with Wales High School about to open its doors, a Swimming Pool became a real prospect once more, along with a Youth Centre. The Youth Centre was built by Bramall & Ogden Ltd of Wath at a cost of £25,246, and was open by the end of June 1971. The Swimming Pool followed soon after, and at much the same time the Art Block seems to have been built.

The Swimming Pool was only partly funded from educational coffers. Among the fundraising attempts was "a hundred mile sponsored walk by approximately twelve 6th formers". The fundraising wasn't limited to DHS. Peter Scott writes: "I remember fundraising for the pool when at Primary School." At the end of 1969, Kiveton Park Rural District Council offered £10,000 for the funding of the pool on the proviso that it could be used by the public, and they later upped this figure to £15,000.

With the Wales project fully off the ground, the powers that be were comparatively responsive to the needs of the school, to the point that they actually asked what it felt was needed in coming development. The school responded in 1971 with the following shopping list: A decent 6th Form study, a laundrette, a Sports Hall, a third library (after the Lower School and Admin Block libraries), increased office space, a bigger staff-room, under-cover accommodation between at least two main blocks (not sure what they're after there, to be honest), and improved changing rooms. In February 1972, the money was released for a Sports Hall, and J A B Short Ltd of Chesterfield were given the job of building it for £76,477.