Hello, from the roads you mention I'm guessing you are looking at the cheaper end of the properties in Letchworth (though actually there's not much on the market at the moment so maybe that's why!).
If so, the options will likely be Grange area (though this is going up in price, a couple of the schools up there have been 'good' for a while), Jackmans (the school there is not so good I've heard and wouldn't recommend the area), a few bits around Hillbrow (though it is near the better secondary and outstanding catholic primary so prices depend on road/house), and on the west side - Abbots, Bursland, Eldefield, Mullway, Hall Mead etc, near Icknield infant school.
We live on the west side. The houses are not the most attractive but good value three-beds. My son will be going to Icknield which I was initially concerned about but they've just had a good Ofsted and I feel a lot more confident about it after going for another information evening.
We moved when I was pregnant with my son (from Hertford which was too expensive!) and I really like the area. There are fantastic parks, a good kids' farm, great indie cinema, the shops are slowly getting better. It is poor for pubs, and restaurant choice isn't great either (go to Hitchin/Baldock for more options!) but that wasn't a priority for us. There's a good community feel and there's loads of events on in the town centre, especially in the summer.
When it comes to moving up the property ladder there are loads of fantastic unique houses here to aspire to, and still cheaper than in any nearby towns :)