• Decoding difficulty. A child can’t be expected to understand the meaning of words s/he was not able to read in the first place.
• Poor reading fluency – slow, laborious, word by word reading. Even if a child can decode well (i.e. s/he can identify words without difficulty), if s/he is not able to do so quickly and automatically it can interfere with comprehension in several ways. Poor reading fluency means it takes more mental energy to decode. The more mental energy one has to put into decoding, the less mental energy one has to put into reading comprehension. That is, the more the student has to think about what the words say, the less “brain power” the student has to think about what the words mean. This can be particularly problematic for students who already have low frustration tolerance, such as students with ADHD, who often are impatient to begin with. Poor reading fluency makes reading even more burdensome for these students. Secondly, an overly slow reading rate makes it more difficult to synthesize the information into a coherent picture of what is being described in the passage. For example, by the time the reader gets to the end of the paragraph, he or she is likely to forget what came at the beginning of the paragraph. This then makes the details one encounters at the end of the passage seem out of context.
• A lack of background knowledge. Reading comprehension can be expected to be greatly impacted if a student does not have any prior knowledge of or experience with the topic. This is why teachers assess background knowledge before assigning passages and provide students with the necessary background knowledge where it is lacking. For example, before delving into Hemingway’s “To Have and Have Not,” the teacher would need to make sure the students have appropriate background knowledge about concepts in the novel, such as the Great Depression, a black market, boating, etc.
• Weak vocabulary. Research has shown that reading is the single biggest predictor of vocabulary development. Therefore, children who avoid reading, including because they have difficulty with it, such as children with dyslexia, are at risk for poor vocabulary. This can create a “snowballing” effect (also sometimes referred to as the “Matthew effect”) in which a lack of reading creates poor vocabulary, and poor vocabulary makes reading more difficult, which causes the child to avoid reading even more, which further stunts vocabulary development, and so on.
• Weak working memory. To over-simplify, working memory can be defined as the ability to keep track of a lot of details in your mind at once, a crucial ability to be able to follow what you’re reading, especially for fact-dense areas like science or social studies. For example, consider the sentence, “John, the son of a wealthy aristocrat, had sold his farmland to pay off a series of debts.” This “one” sentence alone contains at least four details (John is the son of an aristocrat; the aristocrat was wealthy; John sold his farmland; he did so to pay debts).
• Trouble visualizing the passage. The ability to visualize or “build the movie in your mind” of what a passage is describing is a crucial comprehension skill. For example, consider the following statement describing how a brain cell fires: “When a brain cell fires, sodium channels in the cell’s membrane open and sodium ions rush into the cell.” The ability to comprehend a sentence like this one is greatly facilitated if one can generate a mental image of what the sentence is describing, such as thinking of a tube, with passageways like doors on the sides, and sodium ions going through the doors to flood the inside of the cell. Conversely, if one cannot picture sentences such as the one above, one is unlikely to be able to comprehend them.
• Difficulty with saliency determination – the ability to identify relevant details and distinguish them from irrelevant details. Students who struggle with saliency determination have trouble noticing the key details that color the passage with meaning and lead to the main idea. For example, if the main idea of a passage is that a character perseveres, a detail like the fact that she stayed late at work to fix a problem is a relevant detail, as it contributes to the main idea. On the other hand, details like the color of the character’s hair or whether she worked on the 9th floor or 10th floor, that have nothing to do with the main idea, are irrelevant. The ability to tell the difference between such relevant and irrelevant details is an important reading comprehension skill.
• Trouble drawing inferences. This is the ability to “read between the lines” and figure out what was implied but not explicitly stated, such as identifying the main idea or emotional tone of the passage. Drawing an inference requires integrating information or “connecting the dots.” As a simple example, consider a passage that states, “Sally studies. Sally does her homework. Sally participates in class.” By integrating this information, that is, by identifying what is similar across these details, one can form the concept and draw the inference that, “Sally is a good student.” Drawing an inference also requires the student to integrate the text details with his or her background knowledge. Consider for example if a student reads a passage about volcanoes that states that an erupting volcano can cause tidal waves. To make the inference that volcanoes can cause coastal flooding requires that the student connect a specific detail in the text (i.e. that volcanoes can cause tidal waves) with his or her background knowledge (i.e. that tidal waves cause coastal flooding).
• Difficulty paraphrasing and summarizing the passage.

The proper interventions to help children with reading comprehension difficulty follow from a thorough assessment of factors like the ones above to identify why the child is struggling. For example, a child who is having trouble comprehending because of decoding difficulty should receive decoding interventions. A child who is having trouble keeping track of details should be given working memory support, such as “chunking,” which refers to ways of consolidating information to make it more manageable. A child who is having trouble visualizing passages should be taught how to better picture in his or her mind what the passage is describing. A child who is having difficulty integrating information should be taught how to identify relevant details and identify what they have in common. And so on.

There are many, many reading comprehension interventions and programs. The key is to find the strategies that best meet your child’s particular needs as well as to make sure your child’s Individualized Education Program (IEP) goals target the specific aspects of reading comprehension in which your child struggles.