An article was recently published that looks at evaluating First Programming Languages (FPL) the language to use for an introductory course of programming.
An existing issue is that formally assessing a programming language isn't really defined, with a lot of evidence being anecdotal. The proposed evaluation framework looks at technical and environmental feature sets. "The technical feature set covers the language theoretical aspects, whereas, the environmental feature set helps evaluating the external factors." These feature sets are covered in table 2 of the article (link to PDF) and consist of the following:
The article explains each of these points in details, and gives each of the languages being evaluated a rating based on this explanation, followed by a detailed explanation of how the scores of each rating can be compared this includes allowing an evaluator to weigh certain criteria they deem important against the others. As this is for choosing a language to teach someone to program with, different places will have different reasons and goals, so would want to weight things differently.
As the default weight settings do not conform to the original popularity index of the languages, so there should be a different weighting criterion. However, it is very hard to come up with a generic and correct weighting criterion. Therefore, the scoring function should be customizable and the user should be able to tune the weight of each feature based on her preferences. As an example, consider the fact that Ada holds 3rd position in overall scoring, but is not being considered among highly used FPLs as of now.
There is a fairly decent book called Seven Languages in Seven Weeks that uses a similar logic, and I think its very effective. I think the book approaches it a bit better though. You don't really do 7 "hello world" programs, what the author has you do is take a moment to learn the syntax, and then he has you build a completely different program with each language that highlights the power of that specific language. I think this is more effective, as it helps you understand different methods of programming, different ways to approach problems, and understand that each language is built for a purpose. The book teaches you Ruby, Io, Prolog, Scala, Erlang, Clojure, and Haskell, and he details why hes teaching each one. Seven Languages in Seven Weeks [amazon.com]