**We have developed an algorithm for searching by grade level. The core concept in our algorithm is the NAGL (rhymes with bagel). NAGL stands for National Average Grade Level (at which a given concept is taught in the USA).**

**Every term taught in K-16 has a NAGL. By extension a document that is suitable for use in education also has a NAGL.**

**In our ranking algorithm, each document is assigned a NAGL based on the NAGL of the most advanced terminology in the document. The rationale is that students studying at lower grades cannot read the document, because they will not have learned the subject yet. Likewise, those studying at higher grades do not need the document, because they have already studied the subject and learned the concept and terminology. Thus the most advanced terms in the document should correspond to the specific subject under study. If not then the document is incorrectly designed as afar a instruction goes.**

**The NAGL of each term is presently estimated based on analysis of standards of learning from a sample of states. Because the NAGL is an average, students in many cases will be studying a given terminology and subject in a grade other than the NAGL. Other data sources and approaches to estimating the NAGL can be developed, including for other countries. **

**The present NAGL algorithm is developed in the following steps: **

**Inventory the core terminology taught in K-16 science.**
**For each core term, identify the common variants that might be also used as search terms.**
**Determine the grade level at which each core term is taught in the sample state, as specified in the state standards of learning.**
**Average the grade levels from the sample states to get the NAGL for each core term and its variants. **

**The underlying assumption is that terminology and subject matter always correspond. That is, in order to learn about X one has to talk about X. More technically, we define a concept as what one has to know in order to use a term correctly. A concept is therefore a body of knowledge. In any given subject the concepts are part the core knowledge and therefore to learn a subject is to learn its terminology. In short, words embody core knowledge. **