Hi, we rented in the Forest of Dean for a year or so before moving to Gloucester. I've now got one child at primary school in Kingsholm (as I liked the school, and we thought we would be moving there) and another at Ribston Hall near where we live (hooray!).
I think we would have been happy living in Kingsholm, we're certainly getting to know some lovely families around there through the school. Some people warned me off the area because of 'half way houses' and probationary services there (in relation to burglary rates, bikes going missing and so on) but you have to be security conscious anywhere in a city.
Quite a few of my DD's Ribston friends live in Longlevens or Churchdown.
Be aware that almost all children take the bus to the grammar schools in Gloucester - my daughter is one of the very few to walk. A lot have a good hour long bus ride (which is why we moved from the beautiful Forest of Dean). Also, think about which secondary school your various children would go to if they didn't get into grammar school, and consider moving to a catchment area you like the look of, it just relieves the pressure.