This is a double-blind, placebo-controlled, parallel group study in pediatric subjects who have persistent attention impairment following treatment for cancer. This trial has three phases: (1) pre-randomization to establish eligibility, (2) a 12-week, double-blind, placebo-controlled, parallel-group phase with dose escalation based on body weight, (3) a 12-week, blinded extension phase during which all subjects will receive active drug.

The subject and the parent/legal guardian will take part in a screening visit to establish eligibility, and will give informed consent to participate in the study. The parent/legal guardian will be interviewed about the subject's medical history, education status, and medications being taken. The subject and the parent/legal guardian will be given several tests to assess the subject's attention, intelligence, and motor performance skills. A standard set of non-invasive medical examinations and tests will be performed. These interviews and tests will determine whether or not the subject may be eligible to participate.

The eligible subject and his/her parent/legal guardian will come back to the clinical center on the day that the subject is to begin participation in the study. The subject's attention skills will be tested, and the parent/legal guardian will provide related information to the clinic. Vital signs will be assessed. At random, the subject will be assigned to receive either the active drug or placebo, once daily at approximately the same time every day. The study will be "double-blind", meaning that the clinical staff, the subject, and the parent/legal guardian will not know whether the subject is taking active drug or placebo. The parent/legal guardian will be given enough of the study drug or placebo to last for 6 weeks. Doses of active drug will be adjusted according to the subject's body weight.

Three weeks following the baseline visit, the clinic will follow-up by phone to the parent/legal guardian. At 6 and 12 weeks after the subject has started taking the study drug, the subjects and parent/legal guardian will come to the clinic for tests and interviews similar to those at the first visit to the clinic. The parent/legal guardian will receive new supplies of the study drug at each of these clinic visits.

At the time of the 12-week visit, all subjects who had been taking placebo will start taking the active drug and will continue to do so for the remainder of the study, which will last for a total of 24 weeks. The period between 12 and 24 weeks is referred to as the "blinded extension" phase. The subjects who had been taking active drug will continue to do so. At 15 weeks after the subject started taking study drug (3 weeks after all subjects taking placebo are switched to the active drug), another telephone call will be made by the clinic to the parent/legal guardian. At 18 and 24 weeks, the subject and the parent/legal guardian will return to the clinic for tests similar to those at the visits which took place at 6 and 12 weeks. The subject's participation in the study will end at the conclusion of the 24-week visit.

A small amount of blood may be drawn from some subjects during the 12-week, 18-week, and 24-week visits to measure the amount of active drug that is in the subject's bloodstream.

Inclusion Criteria:

1. The subject must have received at least one cycle of chemotherapy and/or cranial radiation, and must have completed this treatment at least one year before screening takes place for entry into this study.
2. Subjects may be male or female; age range: 6 - 17.5 years; weight ≥ 20 kg. They must be physically healthy and able to move about, with or without aids, must be living in the community, and must have adequate motor skills as shown by tests that will be given at the time of screening. The subject's eyesight and hearing must be good enough to allow cooperation with tests and physical examinations. Additionally, they must be able to swallow tablets.
3. There must be subjective complaints by subject and/or parent of difficulties in school or other daily activities, possibly related to impairments in attention. These difficulties must have emerged after treatment for cancer and must still be present 12 months after cessation of treatment. There must also be objective evidence for this impairment, as shown by a test that will be given to the subject at the time of screening.
4. The IQ must be >70 according to tests that will be given at the time of screening.
5. The first language in which the subject learned to read and write must be one that uses Roman lettering (a, b, c, etc.) and Arabic numerals (1, 2, 3, etc.).
6. The subject must not have previously taken any drugs in the class known as cholinesterase inhibitors.
7. A parent or legal guardian must be available who is willing and able to complete all of the outcome measures, to administer medications, and to accompany the subject to the required clinic visits.
8. Subjects with diabetes or thyroid disease may still be eligible if certain medical requirements are satisfied.
9. Female subjects who could become pregnant must undergo pregnancy testing and must agree to use contraception.

Exclusion Criteria:

Subjects who meet any of the following criteria will be excluded from the study:

1. Inability to perform the required tests (for example, because of aphasia, motor deficits affecting the dominant hand, or mental retardation)
2. Motor coordination not sufficient, according to tests to be conducted at the time of screening
3. Recurrence of cancer. If this happens, the subject will have to withdraw from the study.
4. Mental retardation/developmental disability
5. Certain medications, such as methylphenidate, are not allowed during the study.
6. Major depression
7. Problems with the digestive tract that could affect the subject's ability to absorb the study drug
8. Hypersensitivity to a chemical class known as piperidine derivatives
9. Certain other medical conditions as determined by clinical staff
10. Alcoholism, drug abuse, or organic brain disease other than that caused by the cancer or its treatment
11. Pregnancy, nursing, or unwillingness to undergo pregnancy testing if requested by clinical staff
12. Pregnancy, lactation or plans to become pregnant, or unwilling to take a screening ßhCG test if a female >10 years of age.
13. If sexually active, unwillingness to use birth control (males and females)
14. Plans for certain types of elective surgery that would occur while the study is in progress
15. Plans for travel or other events that would interfere with the study schedule
16. Active treatment with another investigational drug within 3 months of the screening visit