Two studies were conducted to compare the performance instability of children (grades 3-9) labeled learning disabled/brain injured (LD/BI) to the performance instability of emotionally handicapped (EH) children. In the first study, 50 LD/BI and 37 EH students were measured on three third grade reading passages twice, once within one sitting and once with the three passages administered during three consecutive weeks. In the second study, a subsample of 43 students (24 LD/BI and 19 EH) were measured on instructional level reading passages 28 to 47 times within 18 school weeks. On the words correct scores on each administration of the third grade passage reading test and on the word correct and errors scores on the instructional level reading passages, standard errors of measurement (SEMs) were calculated and analyses of covariance were run on the SEMs. Results indicated no difference between the performance instability of the two groups of children. Implications for identifying and treating LD/BI and EH students are discussed. (Author/CL)