Excepting grammar, all of the above can be demonstrated via direct observation, usually in a science lab of less than an hour, or through infallible mathematical proofs. Modifcation by descent into completely new Genus' cannot, be definition, because of the time frames reqwired. It has NEVER been observed, but is arrived at by conjecture and extrapolation from variation within a genus (or Biblical kind, more accurately), or speciation. Thus, it requires you take the word of the "expert".
In addition to the NCBI free archive linked above, you can prowl through various biological abstract archives like the one available here; various university molecular and cellular biology archives like the one available here; and various fascinating sites addressing genetics and genetics related evolutionary research, such as the human gene mutation database, the Metazome project, the NCBI human gene master list, the Blast assembled genomes database, and the EMBL nucleotide sequence database You can also, of course, browse through the many fossil databases available, with just a few of them here, here, here, here, here, here, here, here, here, here, here, here, here, here here here and here, and with a pretty good overview of "Paleontological Evidence to Date the Tree of Life" located here.
As you can see from the available literature, evolutionary biology overlaps many scientific fields, including organic chemistry, genetics, paleontology, geology, cell biology, zoology, etc. The point being that there is a great deal of "evidence to weigh," and if high school students will eventually be expected to "weigh" that evidence and "decide for themselves," they will need a solid grounding in it.
This means, of course, a solid grounding not only in biology and the theory of evolution itself, but also in the the scientific fields it draws upon and influences.
"Let the children decide" is all well and good, but give them the children the evidentiary ammunition first so their decision will at least be informed.