We had to wrestle with this question a few years ago, and stakes were very high. TL;DR is to try to appeal to the scientific method. I don't think "online" is

We had to wrestle with this question a few years ago, and stakes were very high. TL;DR is to try to appeal to the scientific method. I don't think "online" is special here. We desperately sought help for our child who was reading at pre-k reading levels while in the 3rd grade. In many US school systems, after 3rd grade, if you haven't acquired basic reading skill, then you are completely screwed: the curriculum moves on. Finding useful information was astonishingly hard -- what we learned is that within the US, an entire industry has evolved around dogmas that are completely uninformed by reproducible research. If you search for reading help, you find appeals to emotion, "this-one-trick-worked-for-me" type books, self-help conferences and such. We also learned that professional teaching programs are built around dogma, and publishing "research" in the field of education requires strict adherence, and does not meaningfully apply hypothesis testing or reproducibility. The practice of reading pedagogy lives in this sweet spot where it kinda-sorta works for just enough students that school districts and admins can assert that kids for whom the system does not work should adjust their expectations in life. We were lucky to discover that reading problems are well understood through neuroscience (not education), and there are decades of reproduced research supporting useful ideas. We were also lucky that my wife happens to be a good teacher (I could never do this!), the two of them get along well, she left her paid job, started homeschooling our child full time, and our child now reads far above grade level.