"It's a recognised fact that SALT in general has been very poor at monitoring and measuring outcomes to evaluate effectivenemss (or otherwise) of intervention."
Do you think we are worse than others suggesting "interventions" in schools in reports following assessments?
It's also dependent on role, this. If you work in a language unit with a small caseload, actually you do huge amounts of monitoring. You monitor and adjust everything you do continually. Do you mean that there is limited gold standard research within the profession? That, of course, is a bit different to monitoring or measuring outcomes related to individual students.
I have only worked in one trust, I'll be honest, so it surprises me when I hear that people don't keep data. What about Nuffield progress charts, or Lidcombe or the adjustments made on a continuing basis in any direct speech sound therapy? 
I assumed that SALTs doing direct therapy kept quite a lot of target-specific data?
To my mind, there is limited outcome measurement on consultative work.. but that's a bit different IMO as so much of the time, half the battle is even getting staff to realise that a child is not just naughty and in need of discipline. To my mind, those therapists who see a child for 45 minutes once a half term (and I have been that therapist) often have a very specific "outcome": see child, assess and write report. This is very carefully documented, of course, in statistical analyses. I am highly sceptical that there can be particularly effective "intervention" in any discipline based on a 45 minute once-half termly visit. The goals shift when provision is that dilute, don't they? Isn't the goal in this type of service delivery more likely to be related to information sharing and training others on SLCN?
I am as harsh a critic of SALT as any, but I don't think that we are particularly any worse than most other professions in the NHS/educational system as is, except in so far that we target some areas that are quite difficult to operationalise.
Social skills "programmes" are one obvious example of this. Social interaction encompasses so many different levels of human experience and development and so many, many variables that it requires not only tremendous skill, experience, creativity and initiative to design a truly effective intervention proramme, but quite a lot of time and a very dedicated consistent treatment team. Knock one cog out of the wheel and you can have a very weak programme indeed.
Typically, "social skills" programmes in schools introduce students to the idea of social convention. Usually, students who have participated in these programmes can tell you a bit more about the mechanics of social interaction at the end of a programme e.g. you need to look at someone, not get n their space etc. Sometimes, this can help them understand the feedback teachers and other adults give them about their behaviour but only rarely is this, in and of itself, going to effect behavioural change. It's a bit like learning about, say, Greek myth. It doesn't make you sprout wings and fly too close to the sun.
If a child is experiencing social difficulties, what is needed is some sort of analysis of what is happening and why, with a strategy related specifically to that.
So, for example, we had a student a number of years ago who would not speak or interact on the playground. So stage 1 of intervention was getting her to actually stand near her peers. Stage 2 was playing alongside her peers in a preferred, nonverbal activity (skipping). Stage 3 was copying her friends in skipping activities. Stage 4 was learning things she could say to her friends when skipping. Stage 5 was saying some of these things to earn rewards.
How did we know when we'd achieved our outcome? Well, simple. She spoke to her friends on the playground. Did this miraculously cure all her social difficulties? Not a chance. It required a huge amount of careful teamwork and planning to do this much, and we were lucky that it generalised into other settings spontaneously. However, as simple as that sounds, it really isn't.. when you consider that even in many language units, SALT time is maybe one hour per child per week (or even less). Unless the team will play ball and there is sufficient time to observe, work out what makes a kid tick and what will enthuse and motivate them without overwhelming them AND sufficient time is given to enable a student to do this again and again many many times day in and day out, it's not likely to happen.
With a speech sound, you can do hundreds of trials in an hour. Social skills are harder to target intensively and peers, in particular, are harder to control as variables. Little buggers.
This doesn't mean that therapists and school personnel shouldn't try. It is a huge bugbear of mine to see ill-defined social targets... but it is a hard, hard thing to do without a hell of a lot of time. Tracking data consistently would be easy peasy if there were adequate resources and data were prioritised, but the reality is schools are frenetic places with many competing priorities and SALTs are usually outsiders whose targets can easily be pushed to one side. Unless the target is very much defined, appropriate, works quickly and the school is 100% on board to carry it out, it can be hard to see change and all too easy to find a dusty programme on a shelf somewhere.
Like moondog, I usually look at frequency of desired behaviour over a set interval. However, that only applies to wholly behavioural targets. With my students, many of whom are verbal and able, I am also looking for signs of cognitive change e.g. developing understanding of why something needs to be done, showing they can recognise complex and abstract behaviour in a structured setting with lots of support long before they are expected to show it with peers. I want them to be able to tell me that they are "getting it" by showing awareness of really quite complex social phenomena as much as be able to do it.. there is so much frustration and anxiety in not understanding the actions of others even after the event that needs to be dealt with as well as actual behaviour. I find it important in my provision that the kids have a chance to talk through all the stuff that stresses them out about the neurotypical too e.g. a student today who wanted to talk about a change in his family circumstance that was distressing him but couldn't understand it unless thoughts and feelings were visually represented.
What is the outcome when we act as "critical friends" for students who are struggling socially due to an inability to navigate the minefield of social relationships? Will it prevent them struggling socially? Not necessarily.. at all.. but it can reduce stress within the school day, particularly at secondary and they do learn vocabulary and ways of talking about these things that may hopefully help them in the future if they need to discuss and destress about these things out with someone (as my AS cousin does online). As well as the behavioural level, there are social and emotional considerations.. I have posted this before, but this reflects my thinking a lot.
You need both IMO..