NACLO is a pencil and paper contest for high school students which involves using analytical skills to solve puzzles in languages that they do not know. In the course of solving the puzzles, students learn something about the structure of human languages and how computers can process them.
Students compete for an opportunity to participate in the invitational round for an opportunity to compete for the US at the International Linguistics Olympiad in Brasilia, or just for fun. (It is really fun!)
What is language, and how does it work? Linguistics is the field of study that explores the nature and structure of language, how it develops and changes, and how it is used to express and evoke meaning.
Core areas of linguistics are the study of non-meaningful parts of language, i.e, sounds and stuff (phonology), the formation of words (morphology), and the structure of meaninful forms above the word level, i.e, phrases and sentences (syntax), and how these relate to language meaning (semantics) and use (pragmatics). Beyond the core are applied fields that examine language types and variations, how people acquire their first and second languages, how people use language to perform acts in the world, how computers process natural languages or are used to study language, and much more.
Yes, the NACLO website has practice problems, each problem is worth a certain number of points where problems worth more points are more difficult: https://naclo.org/practice.php.
Right here: https://naclo.org/registration_page.php
Select Lawrence University as your site and you will be all set.