If there isn't a debate in cycle education between the 'pedal first' or 'balance first' approaches, there should be.
Years ago when I was in Germany and Switzerland and lately in Britain, I notice that pre-schools use bikes without pedals, like the earliest 'dandy-horse', that children sit astride and propel with their feet. There are several makers of these 'balance-bikes'. In the US the Boot Scoot bike is gaining in popularity. The UK Ilsa Bike Rothan is highly praised too. If you want to go green, the Steady Eddy is made of wood. There are many others and in Europe every bike maker seems to have a model in this style.
In my experience, training wheels on pedal bikes cause accidents as they affect the handling, especially on turns.
In fact, I observe training wheels inhibit the brain's natural balance reactions as well as being useless on anything but perfectly level and hard ground. Any engineer will tell you that four points of support is less stable than three points (which a tricycle has) as it gives you two axes to pivot on a variable plane. Just put a four legged stool beside a three legged stool on a tiled floor to see what I mean.
It's a wrong headed approach. You should do everything to naturally develop the child's balance skills and not use ineffective props to try to keep them upright that slow them down.
On a 'balance bike', when kids show they're able to coast and balance and make turns, they can be moved onto a pedal bike. Most kids I've seen adapt to pedals in just a few minutes once the balance is mastered. The challenge for my own children was learning to balance and not managing pedals.
Ahh, then there's the argument that this requires parents to shell out for two bikes, one with and without pedals. You know, at the rate kids grow, you aren't going to get more than a year's life out of a child's bike for a three or four year old. My advice is there's no need to buy a four year old a brand new bike. Every yard sale I see has bikes for this age less than a year old. I bought a lovely second-hand Puky child's bike for £40, taught two children to ride on it and then sold it on for £40.
Instead of fitting training wheels, you could take off the cranks and the chainset on a child's pedal bike, so long as their feet can touch the ground. You could cap the bottom bracket holes easily with pipe-caps until the kid was ready for pedals. Perhaps a bike manufacturer will nick this idea and make the pedals and crank more easily removable on a child's bike. Please, go ahead.
It seems the mindset though that a child needs to start with a 'proper' bike with pedals is firmly established in special needs education. This programme for developmentally disabled children seems to go to extraordinary lengths to teach children to ride by the pedals-first approach. I'd welcome edification on why this approach is preferred over the feet down method. My experience with autistic children and those with dyspraxia, although very limited, shows me that the 'balance-bike' has some advantages there too.
Kate Stirling, president of Boot Scoot Bikes, LLC says: "I have actually had several people contact me, letting me know that they are purchasing for a child with developmental disabilities.
One physical/occupational child therapist contacted me to buy one for her own practice--she said she had been removing pedals for years in order to teach her patients, but they would still hit and scrape their legs where the pedals insert. She was delighted to find our bikes because she could personally afford them for her practice.
Other parents have let me know that they are purchasing for a child with Down's Syndrome. Several parents/grandparents of autistic children have given me rave reviews about how our bikes seemed to give their children a boost in confidence that spilled over into other activities.
I don't have statistics or studies to site so this is just me relaying what has come back to me, but it has been especially fun to hear from these parents who had thought it might just be too hard for their child to learn to ride a traditional bike."
Postscript: I found this website since this posting that pretty much says what I've said as well with a bit more authority.