A sample of 12 recent and older sixth grade social studies textbooks was examined to determine their level of explicitness, one of the criteria used to determine the "friendliness" or comprehensibility of a text. Researchers randomly selected three samples--usually chapters--from each of the 12 textbooks. The Explication Inventory (consisting of six items, each with a five-point scale) was used by two raters to rate each sample, and the ratings for the three samples from each textbook were then averaged to get a total for that text. To check for reliability, a third rater rated the three segments for a random sample of half the textbooks. The results of analysis indicated no statistically significant differences on total explication scores between the recent and the older textbooks. The raters concluded that the social studies textbooks they examined tended to be friendly on the criterion of explicitness, although it should be noted that text friendliness is also affected by extra-text determinants such as student abilities and curricular and instructional factors. (References and tables are provided; appendices consist of the Explication Inventory and a list of the textbooks reviewed.) (AEW)