I have been reading The Panda's Thumb and there is a nice chapter devoted to the discussion of Lamarckism. Essentially the tenets of "Lamarckism" is that evolution can be "directed" by environmental factors, rather than by undirected genetic variation being winnowed out by death or lower reproduction rates of fellow individuals of the species allowing the remaining individuals to pass on genes appropriate to the environmental factors. Lamarckism has been rejected by biologists because "Darwinism" explains all facets of evolution satisfactorily, and no direct evidence of Lamarckism has been discovered, as well as the fact that particular examples (giraffe necks etc.) oft quoted have been discredited as being both explainable by darwinism and having no measurable direct evidence of directed genetic change.
A new approach would be to look at it from a completely different angle as follows. If Lamarckism is a force in evolution, what are the best genetic strategies to follow given a pre-reproductive youth to experiment on what genes are useful and which not. The issue to me is that genes would have to predict what future environments will require. Genetic variation would hedge its bets on an environmental change being a temporary or permanent one. I would suggest that modern controlled experiments on a range of different animals over a large number of generations would demonstrate it. Essentially, almost no experiments have been done since the 1920's and 1930's. With a greater understanding of the complex role of RNA, more nuanced experiments, I believe would find a subtle but pervasive pathway for some direct/accelerated forms of evolution.
Neither the rat/maze learning experiments and antenna/amputation/regrowth experiments have natural environmental analogies, making them less explanatory than they appear. Direct adaptation would only happen where similar changes in environment had happened before in the distant ancestral history of the animal/plant in question. After all, the specific Lamarckian adaptation itself would have to evolve to suit probable dramatic shifts in environment (ie. selection pressures on species that had no Lamarckian adaptation vs species that did)
One particular experiment would be subjecting specimens to permanent darkness. It is a well known evolutionary theme that vision in a large range of beasts becomes impaired when adapted to permanent darkness. It also has reasonably common natural analogy where animals adapted to light have close relatives adapted to dark with common ancestry. Adaptation to permanently, cold, wet, hot or dry are similarly common natural events that lab experiments could weed out direct vs undirected variation.