I live near! We moved to Watford 5 years ago exactly to get more for our money - we were in St. Albans, but when we were thinking of buying a bigger house the St. Albans prices just made our eyes water. Now one child going into Y3 and one about to start reception.
Afraid pretty much everyone doesn't want to send their children to Beechfield because it's actually near some rough areas and the intake is very...mixed council estate. I feel I can say this because when I'd recently moved to Watford and didn't know anyone, I actually visited the nursery there briefly and thought it seemed quite nice. I would say that it's one of the least desirable primaries in Watford. I know this sounds desperately snobby. Sorry.
Callowland park is lovely though. Have you thought of North Watford (nearest schools are Parkgate and Knutsford), or the area round Orchard School, or Abbots or Kings Langley if you fancy a more village-y feel? Knutsford estate (near Watford North train station), or the Tudor area (roads near there with Tudor in the names!) are nice.
Nascot Wood (area and primary school) is very nice but the school is very oversubscribed and houses can be expensive because it's close to town and the train station, and has some lovely properties. Knutsford is also very over subscribed.
You have to be pretty on the ball if you are choosing where to live based on which primary school,you think you'd get a place at - this year, you had to live no more than 386m away to get into Knutsford, and only 237m for Nascot Wood. Stats for each school are all here.
What's your property budget and what are you hoping to get for that?
Happy to answer any other Watford based questions!