Jackson seems to finally be assembling a grammar. Over the past few days we've have the S-V constructions "The man waves" and "Lia* give?" as well as lots of two-word phrases and mimicry. He's not fluent with the "sentences" yet; they're still quite halting and there are beats between the words, but he's definitely assembling more complex speech, so yay!
*Complete with Signing Time name sign for Leah, which is a circled L hand-shape next to the face. :)