There is no absolute answer to this question, as I understand it. What constitutes appropriate early intervention strategies vary enormously from one therapist to the next, form one school to the next, between the social classes & from one culture & religion to the next. Each camp can rally a busload of experts armed with 'scientific' studies validating their approaches. One of the worst I've personally seen the effects of is an extreme form of cognitive/behaviour modification strategy. It is applied to young Auties & it involves rewarding them with something they desire (such as a token system where a certain amount of tokens can be traded for a reward) when they behave in the way the authority figures (parents, teacher, therapist etc) desires & punishments/consequences for 'inappropriate' conduct. Therein lurks the potential for tremendous abuses. Any Aspie/Autie traits get punished. This is akin to trying to de-spectrumize the kid on the spectrum. It is cruel, short-sighted, doomed to fail (since the brain's wiring remains the same) & an exercise in frustration for all involved.
Since the punishing/taking away strategies don't work, frustrated, emotionally & ego invested parents up the ante. Here we've seen many upper middle class to affluent parents really buy into these strategies since they are simple to implement (career people have little time to spend on a challenging child), many are accustomed to being able to buy quick fixes for just about everything & many feel (but don't say it aloud) entitled to have a successful 'chip off the old block' status symbol type of model child. Ironically, Spectrum kids often find more acceptance in families where there is less money since the parents often have fewer lofty expectations, accept that life can be difficult & are less likely to expect to be catered to & buy a solution. Affluent parents often feel humiliated by having someone irregular in their family.
Some types of early intervention are great in that they aim to break the parents' denials that something is different about their child, it isn't a phase & the sooner it is acknowledged & understood, the sooner real strategies & interventions tailored to the specific child & his/her needs can be implemented. Some kids lose their budding ability to speak, interact with others at all & attend to their physical needs. Early interventions that support retaining & improving these skills & scaffolding them to be of use in other areas. A sharp-eyed parent or teacher ought to know what a spectrum kid is interested in & use these interests to engage the child. This is especially effective with Aspie kids since many will go on ad nauseum about the topic they're fascinated with.
Part of the problem with helping people on the spectrum is that the interests of concerned parties are at odds. Parents often go into denial (wasting critical time) & then focus on curing or repairing the child. The teacher has a classroom with over 20 kids in it, pressure to follow a curriculum & ensure that the students meet certain grade standards. With so many kids, the teacher's interest often lies in minimizing any distracting or disruptive behaviours. Other parents too resent the presence of so-called 'retarded' kids in class with their child & the teacher must also defend these kids' rights to be there. When little Jimmy goes home & says that 'that crazy kid' went nuts, threw a fit & class was stopped because of it, the teacher catches the flak. Psychologists want to test their pet theories & there are financial incentives to prescribing drugs. Institutions want to grow their businesses, gain clientele & prestige & often do so using specious cockamamie methods(fear tactics backed by pseudoscience) & making false promises. Religious movements teach that this or that holy guy can cure your (IF the price is right, IF you believe hard enough & IF you stop being such a sinful degenerate). Old school disciplinarians blame it on people being too soft on these kids & believe that spanking (punishing, beating & abusing) these kids will 'learn 'em' to stop with that rocking back & forth.
We Aspies & Auties need to tell of our experiences & express what this spectrum is as we see it. WE need to have more of our own experts & spokes people who can advocate for us. So long as the discourse is directed, generated by & managed from a solely NT perspective, we will continue to be subjected to draconian & ineffective interventions.