While I'm prepared to accept there's a possibility that secondary children may come into a more intellectually impoverished environment & may not have the same resources to draw upon, framing it in terms of IQ is altogether more problematic (if not actually doing more harm than good). It comes down to the inherent inaccuracy & usefulness (or uselessness at a minimum) of the test. What they substantially deal with is the ability to retain & organize data & not much else. This describes a great deal of what computers do. Cleverness, wisdom & most especially the creativity required to achieve these qualities are very poorly measured (if at all). Same for curiosity & intuition (& probably much else). You get the point. There's a lot of agreement on this but some "experts" still have problems not quantifying things with this test. The history of the IQ test drills this home. I remember reading a beautifully researched article in The Atlantic magazine explaining that the inventor of the test was much lauded for it as it was enthusiastically adopted everywhere. After a period of time, he could see it was being misused to categorize people inappropriately & said so - decades before this became common knowledge. The various powers at be unanimously ignored him because they loved the bureaucratic possibilities it represented. In time the problems were acknowledged & numerous "fixes" put in place but the test although much diminished in stature is still sited from some hangers on who have no other ideas on how to make the intangible tangible. The press needs to educate the public more often & deeply that curiosity & creativity are the foundation of intelligence. The latter the only quality that ensures genius (the ability to be visionary by making leaps, sometimes called lateral thinking). IQ tests as stated, are extremely poor at measuring this.

I am the second. My sister and I have virtually the same IQ. She was born about three years before me and excelled in high school, Swarthmore College and proffesional life. Being the second born and going to the same small high school I was constantly compared to my sister by my teachers. I couldn't possibly measure up. I payed for it. I did go to a small private college. I dropped out after one semester. I married a local girl and have been married 26 happy years. My sister was married twice. Her second husband was great. She has three great boys. All successful. I have one daughter also successful. I don't think it is a matter of birth order but simply a matter of parenting skils. There is no reason to treat one child different than the other. My parents were of the age where the first born was more important. I only have the experience of having one child but I think, or I hope to think, if I had any others they others would be treated the same. I think everyone is trying to over analyze the situation and should just offer their children all of the opportunities the parents can afford. And more! I'd also like to know the economic level of the participants and the relation to their scores. A lot of missing info.