I had a similar discussion with GLOOM once.
(It was : why do people call perl a 'script' language ? and it then leads to what is the difference between a 'script language' and a 'language' ?)

Some people think that the difference is the interpreted way is specific to script language : TCL,VB...
But they will not consider JAVA as a script language however (algthough it's an interpreted language)

You can't distinguish them in term of feature, for all scripts languages often have plenty of predefined functions to do high-level operation

It seems that the more common point of view is that if you usually use a language to code big application it's a 'language' but if you usually use it to do short prog it's a 'script language'.
(It seems to be your point of view as you usually use function as soon as the code isn't very small; But be aware that some people use functions even in small script(I do)...)

I think that the difference between script and program are an obsolete thing which came from old age when a script was a custom made with very poor/limited language by opposition to a program which was a lengthy piece of code made in a REAL labguage (COBOL, FORTH...)

IMHO, nowadays the language are so powerful you could produce lengthy and efficient code with almost all (so called) scripts languages...
A script is only often just a program that someone find small.