All waitlists are not created equal.
Take the cases of both Dartmouth and Tufts. In short, Tufts seems not very promising, and Dartmouth seems to offer a slight glimmer of hope.
Tufts does not offer much information publicly. Last year, they did not accept anyone from their wait list. Not even one student. They did not report any information about wait list admits in the prior two years. Tufts does make mention of "typically anywhere from zero to twenty-five" students admitted off the wait list in a blog post (see link below).
Unfortunately, Tufts does not provide its statistics to the College Board, either. However, take a look at the image below, "TUFTS-2015", from the Tufts 2014-2015 Common Data Set paperwork (http://provost.tufts.edu/institutionalresearch/files/CDS_2014-2015.pdf). This is a fact sheet required by the Federal government.
Yes, that is ZERO admits off the wait list from last year's admissions cycle.
For 2013-2014, Tufts chose not to answer. See "TUFTS-2014" below. And they also did not report for 2012-2013. See "TUFTS-2013" below.
Are you seeing the numbers? Or more correctly, the complete lack of them?
If you prefer more clarity than just a few zeros, here is Tufts' page about their wait list, with their advice.
There is more information available on Dartmouth's wait list. The statistics have varied over the past 10+ years from as few as ZERO admits off the wait list to a high of over 100 just last year (2015 fall entry).
Dartmouth College Wait List Statistics (from the College Board)
Fall 2015 entry
Accepted place on waitlist: 963
Offered a place: 129
Fall 2014 entry
Accepted place on wait list: 1133
Offered a place: 0
For more information, and trends over time, see DARTMOUTH -10 YEAR WAIT LIST HISTORY below for a chart showing wait list acceptances from 2003-2013 at Dartmouth, based on numbers released by Dartmouth under mandated Federal guidelines. The article in which this data is found is here: Dartblog: "Waitlist Use Up Again"
There's even more information on Dartmouth's website. An important page to read is this: Waiting List Information | Admissions - which is Dartmouth's procedure for the wait list.
The LinkedIn article below outlines how wait lists are used, and how to approach them. It's lengthy, but filled with great advice from Parke Muth.
TUFTS - 2015
TUFTS - 2014
TUFTS - 2013
DARTMOUTH - 10 YEAR WAIT LIST HISTORY
one set of opinions about being wait listed: