Archive for September, 2009

The New Primary Grade Level

September 21, 2009

By Nirmaldasan

In May 2008, I proposed two conjectures: one for primary-grade texts; and the other for non-primary materials:

* Primary Grade Level (PGL) = W3/10 to W4/10

* Higher Grade Level (HGL) = W4/10 to W5/10

(W3, W4 and W5 are the number of words in 3, 4 and 5 sentences respectively.)

In the present article, I just wish to re-examine the PGL. I tested this word-count formula on several texts and found its performance satisfactory. But it had one drawback. Instead of showing a specific grade level, this word-count formula would show a range from one level (W3/10) to another (W4/10).

To get a specific result, I now propose the New Primary Grade Level (NPGL) = D4/10, based on the number of different words in four sentences (D4). Edward L. Thorndike, Bertha A. Lively, Sidney L. Pressey, Mabel Vogel, Carleton Washburne and other readability experts understood the importance of the number of different words or vocabulary range in determining the grade level of a text.  

Let us test the NPGL on some graded texts (picked up from the appendix in William Dubay’s ‘Working With Plain Language’, being samples drawn from Qualitative Assessment of Text Difficulty, A Practical Guide for Teachers and Writers by Jeanne S. Chall, Glenda L. Bissex, Sue S. Conard, and Susan Harris-Sharples) and compare it with the PGL, Strain Index (S3/10; S3 being the number of syllables in three sentences) and the Spache Readability Index, calculated using the OKAPI! readability tool available online at

Grade 1

A train! A train! A train! A train!

Different words = 2

NPGL = 0.2

PGL = 0.6 to 0.8

Strain Index = 0.6

Spache = 1.12

Grade 2

Farley lived next door to Grover’s garden. He looked out his window and watched Grover planting seeds. Farley called out:

“Hi, Grover! Can I help you plant those seeds?”

“Why certainly, little Farley! Do not forget to wear a sweater,” said Grover.

Different words = 35

NPGL = 3.5

PGL = 2.9 to 4.2

Strain Index = 3.6

Spache = 3.11

Grade 3

Most amphibians lay their eggs in the spring. Most of them lay their eggs in the water.

The female frog lays lots of eggs. Each one has a ball of jelly around it.

Different words = 23

NPGL = 2.3

PGL = 2.4 to 3.3

Strain Index = 2.8

Spache: 2.78

The NPGL grades texts on a scale comprising 1, 2, 3 and 3+ grade levels. The ease of use may recommend this formula as a suitable alternative to the Spache Readability Index.