Depth Needs Breadth
Here are examples (not grade-specific) of what could be required in an English Language Arts course at each of the four levels of the Depth of Knowledge scale, which get progressively "deeper." It's paired with the percentage of the curriculum researchers found at each level for third-graders in about 200 Nevada and Oklahoma schools.*
SOURCE: Hess, Carlock, Jones, & Walkup, (2009). 'What exactly do “fewer, clearer, and higher standards” really look like in the classroom?'
Stuart Cox Jr./Special to The Christian Science Monitor
Above copied from "Is School Too Shallow"
Third grade children are just about to master their reading. Third grade children are just about to learn fractions. Why are we even asking if third grade is "too shallow"? Executive functions are not even fully developed at this age (See control data of Maeder et al. 2016, for example). The Center on the Developing Child at Harvard University reminds us that children need our support so that they could develop their executive functioning skills:
Providing the support that children need to build these skills at home, in early care and education programs, and in other settings they experience regularly is one of society’s most important responsibilities. Growth-promoting environments provide children with “scaffolding” that helps them practice necessary skills before they must perform them alone. Adults can facilitate the development of a child’s executive function skills by establishing routines, modeling social behavior, and creating and maintaining supportive, reliable relationships. It is also important for children to exercise their developing skills through activities that foster creative play and social connection, teach them how to cope with stress, involve vigorous exercise, and over time, provide opportunities for directing their own actions with decreasing adult supervision.Judging whether a school is too shallow or not by simply examining its curriculum and weighing how much extended reasoning is present is actually what is shallow. Young children need a lot of support as they develop their cognitive skills. Education needs to be timely and appropriate.
Working as a researcher, I need to know my area in great depth. Outside of the laboratory, it is much more helpful to know a wide variety of subjects. It helps in talking and therefore socializing with other people. It helps in addressing daily chores or even challenges. Children need these as well. There is plenty of time after the elementary years to dive into critical thinking.